Currently, the setup.py script detects the clang compiler only when invoked
with CC=clang. But when using a specific version (e.g. CC=clang-11), this
doesn't work correctly and wrong compiler flags are set, leading to build
errors.

To properly detect clang, invoke the compiler with -v and check the output.
The first line should start with "clang version ...".

Committer testing:

  $ make CC=clang-9 O=/tmp/build/perf -C tools/perf install-bin
  <SNIP>
  $ readelf -wi /tmp/build/perf/python/perf.cpython-37m-x86_64-linux-gnu.so | grep DW_AT_producer | head -1
    <c>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 9.0.1 (Fedora 9.0.1-2.fc31) /usr/bin/clang-9 -Wno-unused-result -Wsign-compare -D DYNAMIC_ANNOTATIONS_ENABLED=1 -D NDEBUG -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-command-line -m64 -mtune=generic -fasynchronous-unwind-tables -fcf-protection=full -D _GNU_SOURCE -fPIC -fwrapv -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked -Wredundant-decls -Wstrict-prototypes -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -Wshadow -D HAVE_ARCH_X86_64_SUPPORT -I /tmp/build/perf/arch/x86/include/generated -D HAVE_SYSCALL_TABLE_SUPPORT -D HAVE_PERF_REGS_SUPPORT -D HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET -Werror -O3 -fno-omit-frame-pointer -ggdb3 -funwind-tables -Wall -Wextra -std=gnu99 -fstack-protector-all -D _FORTIFY_SOURCE=2 -D _LARGEFILE64_SOURCE -D _FILE_OFFSET_BITS=64 -D _GNU_SOURCE -I /home/acme/git/perf/tools/lib/perf/include -I /home/acme/git/perf/tools/perf/util/include -I /home/acme/git/perf/tools/perf/arch/x86/include -I /home/acme/git/perf/tools/include/ -I /home/acme/git/perf/tools/arch/x86/include/uapi -I /home/acme/git/perf/tools/include/uapi -I /home/acme/git/perf/tools/arch/x86/include/ -I /home/acme/git/perf/tools/arch/x86/ -I /tmp/build/perf//util -I /tmp/build/perf/ -I /home/acme/git/perf/tools/perf/util -I /home/acme/git/perf/tools/perf -I /home/acme/git/perf/tools/lib/ -D HAVE_PTHREAD_ATTR_SETAFFINITY_NP -D HAVE_PTHREAD_BARRIER -D HAVE_EVENTFD -D HAVE_GET_CURRENT_DIR_NAME -D HAVE_GETTID -D HAVE_DWARF_GETLOCATIONS_SUPPORT -D HAVE_GLIBC_SUPPORT -D HAVE_AIO_SUPPORT -D HAVE_SCHED_GETCPU_SUPPORT -D HAVE_SETNS_SUPPORT -D HAVE_LIBELF_SUPPORT -D HAVE_LIBELF_MMAP_SUPPORT -D HAVE_ELF_GETPHDRNUM_SUPPORT -D HAVE_GELF_GETNOTE_SUPPORT -D HAVE_ELF_GETSHDRSTRNDX_SUPPORT -D HAVE_DWARF_SUPPORT -D HAVE_LIBBPF_SUPPORT -D HAVE_BPF_PROLOGUE -D HAVE_SDT_EVENT -D HAVE_JITDUMP -D HAVE_DWARF_UNWIND_SUPPORT -D NO_LIBUNWIND_DEBUG_FRAME -D HAVE_LIBUNWIND_SUPPORT -D HAVE_LIBCRYPTO_SUPPORT -D HAVE_SLANG_SUPPORT -D HAVE_GTK2_SUPPORT -D NO_LIBPERL -D HAVE_TIMERFD_SUPPORT -D HAVE_LIBPYTHON_SUPPORT -D HAVE_CPLUS_DEMANGLE_SUPPORT -D HAVE_LIBBFD_SUPPORT -D HAVE_ZLIB_SUPPORT -D HAVE_LZMA_SUPPORT -D HAVE_ZSTD_SUPPORT -D HAVE_LIBCAP_SUPPORT -D HAVE_BACKTRACE_SUPPORT -D HAVE_LIBNUMA_SUPPORT -D HAVE_KVM_STAT_SUPPORT -D DISASM_FOUR_ARGS_SIGNATURE -D HAVE_LIBBABELTRACE_SUPPORT -D HAVE_AUXTRACE_SUPPORT -D HAVE_JVMTI_CMLR -I /tmp/build/perf/ -fPIC -I util/include -I /usr/include/python3.7m -c /home/acme/git/perf/tools/perf/util/python.c -o /tmp/build/perf/python_ext_build/tmp/home/acme/git/perf/tools/perf/util/python.o -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked -Wredundant-decls -Wstrict-prototypes -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -Wshadow -D HAVE_ARCH_X86_64_SUPPORT -I /tmp/build/perf/arch/x86/include/generated -D HAVE_SYSCALL_TABLE_SUPPORT -D HAVE_PERF_REGS_SUPPORT -D HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET -Werror -O3 -fno-omit-frame-pointer -ggdb3 -funwind-tables -Wall -Wextra -std=gnu99 -fstack-protector-all -D _FORTIFY_SOURCE=2 -D _LARGEFILE64_SOURCE -D _FILE_OFFSET_BITS=64 -D _GNU_SOURCE -I /home/acme/git/perf/tools/lib/perf/include -I /home/acme/git/perf/tools/perf/util/include -I /home/acme/git/perf/tools/perf/arch/x86/include -I /home/acme/git/perf/tools/include/ -I /home/acme/git/perf/tools/arch/x86/include/uapi -I /home/acme/git/perf/tools/include/uapi -I /home/acme/git/perf/tools/arch/x86/include/ -I /home/acme/git/perf/tools/arch/x86/ -I /tmp/build/perf//util -I /tmp/build/perf/ -I /home/acme/git/perf/tools/perf/util -I /home/acme/git/perf/tools/perf -I /home/acme/git/perf/tools/lib/ -D HAVE_PTHREAD_ATTR_SETAFFINITY_NP -D HAVE_PTHREAD_BARRIER -D HAVE_EVENTFD -D HAVE_GET_CURRENT_DIR_NAME -D HAVE_GETTID -D HAVE_DWARF_GETLOCATIONS_SUPPORT -D HAVE_GLIBC_SUPPORT -D HAVE_AIO_SUPPORT -D HAVE_SCHED_GETCPU_SUPPORT -D HAVE_SETNS_SUPPORT -D HAVE_LIBELF_SUPPORT -D HAVE_LIBELF_MMAP_SUPPORT -D HAVE_ELF_GETPHDRNUM_SUPPORT -D HAVE_GELF_GETNOTE_SUPPORT -D HAVE_ELF_GETSHDRSTRNDX_SUPPORT -D HAVE_DWARF_SUPPORT -D HAVE_LIBBPF_SUPPORT -D HAVE_BPF_PROLOGUE -D HAVE_SDT_EVENT -D HAVE_JITDUMP -D HAVE_DWARF_UNWIND_SUPPORT -D NO_LIBUNWIND_DEBUG_FRAME -D HAVE_LIBUNWIND_SUPPORT -D HAVE_LIBCRYPTO_SUPPORT -D HAVE_SLANG_SUPPORT -D HAVE_GTK2_SUPPORT -D NO_LIBPERL -D HAVE_TIMERFD_SUPPORT -D HAVE_LIBPYTHON_SUPPORT -D HAVE_CPLUS_DEMANGLE_SUPPORT -D HAVE_LIBBFD_SUPPORT -D HAVE_ZLIB_SUPPORT -D HAVE_LZMA_SUPPORT -D HAVE_ZSTD_SUPPORT -D HAVE_LIBCAP_SUPPORT -D HAVE_BACKTRACE_SUPPORT -D HAVE_LIBNUMA_SUPPORT -D HAVE_KVM_STAT_SUPPORT -D DISASM_FOUR_ARGS_SIGNATURE -D HAVE_LIBBABELTRACE_SUPPORT -D HAVE_AUXTRACE_SUPPORT -D HAVE_JVMTI_CMLR -I /tmp/build/perf/ -fno-strict-aliasing -Wno-write-strings -Wno-unused-parameter -Wno-redundant-decls
  $

And here is how tools/perf/util/setup.py checks if the used clang has
options that the distro specific python extension building compiler
defaults:

  if cc_is_clang:
      from distutils.sysconfig import get_config_vars
      vars = get_config_vars()
      for var in ('CFLAGS', 'OPT'):
          vars[var] = sub("-specs=[^ ]+", "", vars[var])
          if not clang_has_option("-mcet"):
              vars[var] = sub("-mcet", "", vars[var])
          if not clang_has_option("-fcf-protection"):
              vars[var] = sub("-fcf-protection", "", vars[var])
          if not clang_has_option("-fstack-clash-protection"):
              vars[var] = sub("-fstack-clash-protection", "", vars[var])
          if not clang_has_option("-fstack-protector-strong"):
              vars[var] = sub("-fstack-protector-strong", "", vars[var])

So "-fcf-protection=full" is used, clang-9 has this option and thus it
was kept, the perf python extension was built with it and the build
completed successfully.

Link: https://github.com/ClangBuiltLinux/linux/issues/903Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Igor Lubashev <ilubashe@akamai.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: clang-built-linux@googlegroups.com
Link: http://lore.kernel.org/lkml/20200309085618.14307-1-ilie.halip@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>