Revert "um: clang: Strip out -mno-global-merge from USER_CFLAGS"

This reverts commit 6580c5c18fb3df2b11c5e0452372f815deeff895.

This patch is buggy, as noted in the patch linked below. The root cause
has been solved by removing '-mno-global-merge' for the entire kernel.

Link: https://lore.kernel.org/r/[e-mail]/
Signed-off-by: Nathan Chancellor <[e-mail]>
Reviewed-by: David Gow <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

arch/um/Makefile

···
 		-D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \
 		-idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__
 
-ifdef CONFIG_CC_IS_CLANG
-USER_CFLAGS := $(patsubst -mno-global-merge,,$(USER_CFLAGS))
-endif
-
 #This will adjust *FLAGS accordingly to the platform.
 include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS)