tools: Suppress request for warning options not existent in clang

To allow building with clang, avoiding:

  error: unknown warning option '-Wstrict-aliasing=3'; did you mean '-Wstring-plus-int'? [-Werror,-Wunknown-warning-option]

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-xvthlvmhzfnt7jx73jgmaea1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/scripts/Makefile.include

@@ -32,7 +32,6 @@ EXTRA_WARNINGS += -Wold-style-definition
 EXTRA_WARNINGS += -Wpacked
 EXTRA_WARNINGS += -Wredundant-decls
 EXTRA_WARNINGS += -Wshadow
-EXTRA_WARNINGS += -Wstrict-aliasing=3
 EXTRA_WARNINGS += -Wstrict-prototypes
 EXTRA_WARNINGS += -Wswitch-default
 EXTRA_WARNINGS += -Wswitch-enum
@@ -40,6 +39,10 @@ EXTRA_WARNINGS += -Wundef
 EXTRA_WARNINGS += -Wwrite-strings
 EXTRA_WARNINGS += -Wformat
 
+ifneq ($(CC), clang)
+EXTRA_WARNINGS += -Wstrict-aliasing=3
+endif
+
 ifneq ($(findstring $(MAKEFLAGS), w),w)
 PRINT_DIR = --no-print-directory
 else