efi: libstub: Deduplicate ftrace command line argument filtering

No need for the same pattern to be used four times for each architecture
individually if we can just apply it once later.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/Makefile

@@ -5,6 +5,10 @@
 # things like ftrace and stack-protector are likely to cause trouble if left
 # enabled, even if doing so doesn't break the build.
 #
+
+# non-x86 reuses KBUILD_CFLAGS, x86 does not
+cflags-y			:= $(KBUILD_CFLAGS)
+
 cflags-$(CONFIG_X86_32)		:= -march=i386
 cflags-$(CONFIG_X86_64)		:= -mcmodel=small
 cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
@@ -18,20 +22,17 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
 
 # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
 # disable the stackleak plugin
-cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fpie $(DISABLE_STACKLEAK_PLUGIN) \
+cflags-$(CONFIG_ARM64)		+= -fpie $(DISABLE_STACKLEAK_PLUGIN) \
 				   $(call cc-option,-mbranch-protection=none)
-cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fno-builtin -fpic \
+cflags-$(CONFIG_ARM)		+= -fno-builtin -fpic \
 				   $(call cc-option,-mno-single-pic-base)
-cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fpic
-cflags-$(CONFIG_LOONGARCH)	:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fpie
+cflags-$(CONFIG_RISCV)		+= -fpic
+cflags-$(CONFIG_LOONGARCH)	+= -fpie
 
 cflags-$(CONFIG_EFI_PARAMS_FROM_FDT)	+= -I$(srctree)/scripts/dtc/libfdt
 
-KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
+KBUILD_CFLAGS			:= $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
+				   -Os -DDISABLE_BRANCH_PROFILING \
 				   -include $(srctree)/include/linux/hidden.h \
 				   -D__NO_FORTIFY \
 				   -ffreestanding \