kbuild: remove cc-option test of -Werror=date-time

The minimal compiler versions, GCC 4.9 and Clang 10 support this flag.

Here is the godbolt:
https://godbolt.org/z/xvjcMa

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Will Deacon <will@kernel.org>

Makefile

@@ -946,7 +946,7 @@ KBUILD_CFLAGS  += -fno-stack-check
 KBUILD_CFLAGS   += $(call cc-option,-fconserve-stack)
 
 # Prohibit date/time macros, which would make the build non-deterministic
-KBUILD_CFLAGS   += $(call cc-option,-Werror=date-time)
+KBUILD_CFLAGS   += -Werror=date-time
 
 # enforce correct pointer usage
 KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)

arch/arm64/kernel/vdso32/Makefile

@@ -92,7 +92,7 @@ VDSO_CFLAGS += $(call cc32-option,-Wdeclaration-after-statement,)
 VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
 VDSO_CFLAGS += -fno-strict-overflow
 VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
-VDSO_CFLAGS += $(call cc32-option,-Werror=date-time)
+VDSO_CFLAGS += -Werror=date-time
 VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types)
 
 # The 32-bit compiler does not provide 128-bit integers, which are used in