[PATCH 1/1] perf build: Remove -Wno-unused-but-set-variable from the flex flags when building with clang < 13.0.0

[Arnaldo Carvalho de Melo]

clang < 13.0.0 doesn't grok -Wno-unused-but-set-variable, so just remove
it to avoid:

  error: unknown warning option '-Wno-unused-but-set-variable'; did you mean '-Wno-unused-const-variable'? [-Werror,-Wunknown-warning-option]
  make[4]: *** [/git/perf-6.5.0-rc4/tools/build/Makefile.build:128: /tmp/build/perf/util/pmu-flex.o] Error 1
  make[4]: *** Waiting for unfinished jobs....

Fixes: ddc8e4c966923ad1 ("perf build: Disable fewer bison warnings")
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/Build | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index d487aec0b458a0d9..a9051ab2d52ac926 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -1,3 +1,4 @@
+include $(srctree)/tools/scripts/Makefile.include
 include $(srctree)/tools/scripts/utilities.mak
 
 perf-y += arm64-frame-pointer-unwind-support.o
@@ -311,6 +312,15 @@ CFLAGS_bpf-filter-flex.o    += $(flex_flags)
 #  int yynerrs = 0;
 
 bison_flags := -DYYENABLE_NLS=0 -Wno-unused-but-set-variable
+
+# Old clangs don't grok -Wno-unused-but-set-variable, remove it
+ifeq ($(CC_NO_CLANG), 0)
+  CLANG_VERSION := $(shell $(CLANG) --version | head -1 | sed 's/.*clang version \([[:digit:]]\+.[[:digit:]]\+.[[:digit:]]\+\).*/\1/g')
+  ifeq ($(call version-lt3,$(CLANG_VERSION),13.0.0),1)
+    bison_flags := $(subst -Wno-unused-but-set-variable,,$(bison_flags))
+  endif
+endif
+
 BISON_GE_382 := $(shell expr $(shell $(BISON) --version | grep bison | sed -e 's/.\+ \([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\1\2\3/g') \>\= 382)
 ifeq ($(BISON_GE_382),1)
   bison_flags += -Wno-switch-enum
-- 
2.37.1