arm64: ftrace: Don't forbid CALL_OPS+CC_OPTIMIZE_FOR_SIZE with Clang

Per commit b3f11af ("arm64: ftrace: forbid CALL_OPS with
CC_OPTIMIZE_FOR_SIZE"), GCC is silently ignoring `-falign-functions=N`
when passed `-Os`, causing functions to be improperly aligned. This
doesn't seem to be a problem with Clang though, where enabling CALL_OPS
with CC_OPTIMIZE_FOR_SIZE doesn't spit out any warnings at boot about
misaligned patch-sites. Only forbid CALL_OPS if GCC is used and we're
optimizing for size so that CALL_OPS can be used with clang optimizing
for size.

Cc: Jason Ling <[email protected]>
Cc: Florian Fainelli <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: [email protected]
Fixes: b3f11af ("arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE")
Signed-off-by: Stephen Boyd <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

arch/arm64/Kconfig

@@ -198,7 +198,7 @@ config ARM64
 		if DYNAMIC_FTRACE_WITH_ARGS && DYNAMIC_FTRACE_WITH_CALL_OPS
 	select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
 		if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG && \
-		    !CC_OPTIMIZE_FOR_SIZE)
+		    (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
 		if DYNAMIC_FTRACE_WITH_ARGS
 	select HAVE_SAMPLE_FTRACE_DIRECT