perf python: Fix clang detection to strip out options passed in $CC

The clang check in the python setup.py file expected $CC to be just the
name of the compiler, not the compiler + options, i.e. all options were
expected to be passed in $CFLAGS, this ends up making it fail in systems
where CC is set to, e.g.:

 "aarch64-linaro-linux-gcc --sysroot=/oe/build/tmp/work/juno-linaro-linux/perf/1.0-r9/recipe-sysroot"

Like this:

  $ python3
  >>> from subprocess import Popen
  >>> a = Popen(["aarch64-linux-gnu-gcc --sysroot=/oe/build/tmp/work/juno-linaro-linux/perf/1.0-r9/recipe-sysroot", "-v"])
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "/usr/lib/python3.6/subprocess.py", line 729, in __init__
      restore_signals, start_new_session)
    File "/usr/lib/python3.6/subprocess.py", line 1364, in _execute_child
      raise child_exception_type(errno_num, err_msg, err_filename)
  FileNotFoundError: [Errno 2] No such file or directory: 'aarch64-linux-gnu-gcc --sysroot=/oe/build/tmp/work/juno-linaro-linux/perf/1.0-r9/recipe-sysroot': 'aarch64-linux-gnu-gcc --sysroot=/oe/build/tmp/work/juno-linaro-linux/perf/1.0-r9/recipe-sysroot'
  >>>

Make it more robust, covering this case, by passing cc.split()[0] as the
first arg to popen().

Fixes: a7ffd416 ("perf python: Fix clang detection when using CC=clang-version")
Reported-by: Daniel Díaz <daniel.diaz@linaro.org>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Daniel Díaz <daniel.diaz@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ilie Halip <ilie.halip@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/20200401124037.GA12534@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/setup.py

@@ -3,7 +3,7 @@ from subprocess import Popen, PIPE
 from re import sub
 
 cc = getenv("CC")
-cc_is_clang = b"clang version" in Popen([cc, "-v"], stderr=PIPE).stderr.readline()
+cc_is_clang = b"clang version" in Popen([cc.split()[0], "-v"], stderr=PIPE).stderr.readline()
 
 def clang_has_option(option):
     return [o for o in Popen([cc, option], stderr=PIPE).stderr.readlines() if b"unknown argument" in o] == [ ]