powerpc/xmon: Reapply "Relax frame size for clang"

This is a manual revert of commit 7f3c5d09 ("Revert "powerpc/xmon:
Relax frame size for clang"") but using ccflags-$(CONFIG_CC_IS_CLANG)
which is shorter.

Turns out that this is reproducible still under specific compiler
versions (mea culpa: I did not test every supported version of clang),
and even a few randconfigs bots found.

We'll have to revisit this again in the future, for now back this out.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/252#issuecomment-1690371256Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/llvm/202308260344.Vc4Giuk7-lkp@intel.com/Suggested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230828-ppc_rerevert-v2-1-46b71a3656c6@google.com

arch/powerpc/xmon/Makefile

@@ -12,6 +12,10 @@ ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
 
 ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
 
+# Clang stores addresses on the stack causing the frame size to blow
+# out. See https://github.com/ClangBuiltLinux/linux/issues/252
+ccflags-$(CONFIG_CC_IS_CLANG) += -Wframe-larger-than=4096
+
 obj-y			+= xmon.o nonstdio.o spr_access.o xmon_bpts.o
 
 ifdef CONFIG_XMON_DISASSEMBLY