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

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

Per commit b3f11af9b2ce ("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 <jasonling@chromium.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: llvm@lists.linux.dev
Fixes: b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240223064032.3463229-1-swboyd@chromium.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>