tools: Factor Clang, LLC and LLVM utils definitions

When dealing with BPF/BTF/pahole and DWARF v5 I wanted to build bpftool.

While looking into the source code I found duplicate assignments in misc tools
for the LLVM eco system, e.g. clang and llvm-objcopy.

Move the Clang, LLC and/or LLVM utils definitions to tools/scripts/Makefile.include
file and add missing includes where needed. Honestly, I was inspired by the commit
c8a950d0 ("tools: Factor HOSTCC, HOSTLD, HOSTAR definitions").

I tested with bpftool and perf on Debian/testing AMD64 and LLVM/Clang v11.1.0-rc1.

Build instructions:

[ make and make-options ]
MAKE="make V=1"
MAKE_OPTS="HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang LD=ld.lld LLVM=1 LLVM_IAS=1"
MAKE_OPTS="$MAKE_OPTS PAHOLE=/opt/pahole/bin/pahole"

[ clean-up ]
$MAKE $MAKE_OPTS -C tools/ clean

[ bpftool ]
$MAKE $MAKE_OPTS -C tools/bpf/bpftool/

[ perf ]
PYTHON=python3 $MAKE $MAKE_OPTS -C tools/perf/

I was careful with respecting the user's wish to override custom compiler, linker,
GNU/binutils and/or LLVM utils settings.
Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com> # tools/build and tools/perf
Link: https://lore.kernel.org/bpf/20210128015117.20515-1-sedat.dilek@gmail.com

tools/bpf/bpftool/Makefile

@@ -75,8 +75,6 @@ endif
 
 INSTALL ?= install
 RM ?= rm -f
-CLANG ?= clang
-LLVM_STRIP ?= llvm-strip
 
 FEATURE_USER = .bpftool
 FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib libcap \

tools/bpf/runqslower/Makefile

@@ -3,9 +3,6 @@ include ../../scripts/Makefile.include
 
 OUTPUT ?= $(abspath .output)/
 
-CLANG ?= clang
-LLC ?= llc
-LLVM_STRIP ?= llvm-strip
 BPFTOOL_OUTPUT := $(OUTPUT)bpftool/
 DEFAULT_BPFTOOL := $(BPFTOOL_OUTPUT)bpftool
 BPFTOOL ?= $(DEFAULT_BPFTOOL)

tools/build/feature/Makefile

 # SPDX-License-Identifier: GPL-2.0
+include ../../scripts/Makefile.include
+
 FILES=                                          \
          test-all.bin                           \
          test-backtrace.bin                     \
@@ -76,8 +78,6 @@ FILES=                                          \
 FILES := $(addprefix $(OUTPUT),$(FILES))
 
 PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
-LLVM_CONFIG ?= llvm-config
-CLANG ?= clang
 
 all: $(FILES)
 

tools/perf/Makefile.perf

@@ -176,7 +176,6 @@ endef
 LD += $(EXTRA_LDFLAGS)
 
 PKG_CONFIG = $(CROSS_COMPILE)pkg-config
-LLVM_CONFIG ?= llvm-config
 
 RM      = rm -f
 LN      = ln -f

tools/scripts/Makefile.include

@@ -69,6 +69,13 @@ HOSTCC  ?= gcc
 HOSTLD  ?= ld
 endif
 
+# Some tools require Clang, LLC and/or LLVM utils
+CLANG		?= clang
+LLC		?= llc
+LLVM_CONFIG	?= llvm-config
+LLVM_OBJCOPY	?= llvm-objcopy
+LLVM_STRIP	?= llvm-strip
+
 ifeq ($(CC_NO_CLANG), 1)
 EXTRA_WARNINGS += -Wstrict-aliasing=3
 endif

tools/testing/selftests/bpf/Makefile

@@ -19,8 +19,6 @@ ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
 endif
 
-CLANG		?= clang
-LLVM_OBJCOPY	?= llvm-objcopy
 BPF_GCC		?= $(shell command -v bpf-gcc;)
 SAN_CFLAGS	?=
 CFLAGS += -g -rdynamic -Wall -O2 $(GENFLAGS) $(SAN_CFLAGS)		\

tools/testing/selftests/tc-testing/Makefile

 # SPDX-License-Identifier: GPL-2.0
+include ../../../scripts/Makefile.include
 
 top_srcdir = $(abspath ../../../..)
 APIDIR := $(top_scrdir)/include/uapi
@@ -7,8 +8,6 @@ TEST_GEN_FILES = action.o
 KSFT_KHDR_INSTALL := 1
 include ../lib.mk
 
-CLANG ?= clang
-LLC   ?= llc
 PROBE := $(shell $(LLC) -march=bpf -mcpu=probe -filetype=null /dev/null 2>&1)
 
 ifeq ($(PROBE),)