[PATCH v2 04/18] tools scripts: Short-circuit CC_NO_CLANG compiler probe in Makefile.include

[Ian Rogers]

In Makefile.include, CC_NO_CLANG unconditionally executed a GCC/Clang
compiler inspection fork (gcc -dM -E ...) during Makefile parse time.
Because Makefile.include is included across more than 40 sub-makes and
component directories throughout the Kbuild tree, Make continuously
re-executed this compiler probe dozens of times during incremental builds.

Wrap CC_NO_CLANG with a conditional check and export the variable to
sub-makes. This guarantees Kbuild evaluates the compiler backend exactly
once during top-level Make invocation, eliminating 40+ redundant shell forks
across the build tree.

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/scripts/Makefile.include | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 41971a68972d..3c7803122ae2 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -74,7 +74,10 @@ $(call allow-override,CXX,$(CROSS_COMPILE)g++)
 $(call allow-override,STRIP,$(CROSS_COMPILE)strip)
 endif
 
+ifeq ($(CC_NO_CLANG),)
 CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
+endif
+export CC_NO_CLANG
 
 ifneq ($(LLVM),)
 HOSTAR  ?= $(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX)
-- 
2.54.0.563.g4f69b47b94-goog