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

This is a manual revert of commit 7f3c5d0 ("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 <[email protected]>
Closes: ClangBuiltLinux#252 (comment)
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/llvm/[email protected]/
Suggested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

Author: nickdesaulniers

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