kbuild: use CONFIG_CC_VERSION_TEXT to construct LINUX_COMPILER macro

scripts/mkcompile_h runs $(CC) just for getting the version string.
Reuse CONFIG_CC_VERSION_TEXT for optimization.

For GCC, this slightly changes the version string. I do not think it
is a big deal as we do not have the defined format for LINUX_COMPILER.
In fact, the recent commit 4dcc9a88 ("kbuild: mkcompile_h:
Include $LD version in /proc/version") added the linker version.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

init/Makefile

@@ -35,4 +35,4 @@ include/generated/compile.h: FORCE
 	@$($(quiet)chk_compile.h)
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@	\
 	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)"	\
-	"$(CONFIG_PREEMPT_RT)" "$(CC)" "$(LD)"
+	"$(CONFIG_PREEMPT_RT)" $(CONFIG_CC_VERSION_TEXT) "$(LD)"

scripts/mkcompile_h

@@ -6,7 +6,7 @@ ARCH=$2
 SMP=$3
 PREEMPT=$4
 PREEMPT_RT=$5
-CC=$6
+CC_VERSION="$6"
 LD=$7
 
 vecho() { [ "${quiet}" = "silent_" ] || echo "$@" ; }
@@ -62,7 +62,6 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
   printf '#define LINUX_COMPILE_BY "%s"\n' "$LINUX_COMPILE_BY"
   echo \#define LINUX_COMPILE_HOST \"$LINUX_COMPILE_HOST\"
 
-  CC_VERSION=$($CC -v 2>&1 | grep ' version ' | sed 's/[[:space:]]*$//')
   LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
 		      | sed 's/[[:space:]]*$//')
   printf '#define LINUX_COMPILER "%s"\n' "$CC_VERSION, $LD_VERSION"