x86/build: Remove old -funit-at-a-time GCC quirk

The following commit:

  e501ce957a78 ("x86: Force asm-goto")

... bumped the minimum GCC version to 4.5 for building the x86 kernel.

arch/x86/Makefile no longer needs to take care of older GCC versions,
such as this pre-4.0 -funit-at-a-time quirk.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1531138041-24200-1-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Makefile

@@ -80,11 +80,6 @@ ifeq ($(CONFIG_X86_32),y)
         # alignment instructions.
         KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align4))
 
-        # Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
-        # a lot more stack due to the lack of sharing of stacklots:
-        KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0400, \
-				$(call cc-option,-fno-unit-at-a-time))
-
         # CPU-specific tuning. Anything which can be shared with UML should go here.
         include arch/x86/Makefile_32.cpu
         KBUILD_CFLAGS += $(cflags-y)