Filter out '-std=gnu99' when running the assembler. This causes an error

when building MIPS that looks like this:

libc/string/mips/memcpy.S:156:1: pasting "memcpy" and ":" does not give
a valid preprocessing token
make[1]: *** [libc/string/mips/memcpy.os] Error 1

Even if this does not cause an error on other architectures, this option
should not be having an effect on preprocessed assembly code.

Makerules

@@ -96,7 +96,7 @@ disp_ar        = $($(DISP)_disp_ar)
 disp_ld        = $($(DISP)_disp_ld)
 
 cmd_compile.c = $(CC) -c $< -o $@ $(CFLAGS) $(ARCH_CFLAGS) $(CFLAGS-$(suffix $@)) $(filter-out $(CFLAGS-OMIT-$(notdir $<)),$(CFLAGS-$(notdir $(^D)))) $(CFLAGS-$(subst $(top_srcdir),,$(dir $<))) $(CFLAGS-$(notdir $<)) $(CFLAGS-$(notdir $@))
-cmd_compile.S = $(cmd_compile.c) -D__ASSEMBLER__ $(ASFLAGS) $(ARCH_ASFLAGS) $(ASFLAGS-$(suffix $@)) $(ASFLAGS-$(notdir $<)) $(ASFLAGS-$(notdir $@))
+cmd_compile.S = $(filter-out -std=gnu99, $(cmd_compile.c)) -D__ASSEMBLER__ $(ASFLAGS) $(ARCH_ASFLAGS) $(ASFLAGS-$(suffix $@)) $(ASFLAGS-$(notdir $<)) $(ASFLAGS-$(notdir $@))
 cmd_compile.m = $(cmd_compile.c) -DL_$(patsubst %$(suffix $(notdir $@)),%,$(notdir $@))
 cmd_compile-m = $(CC) $^ -c -o $@ $(CFLAGS) $(ARCH_CFLAGS) $(CFLAGS-$(suffix $@)) $(CFLAGS-$(notdir $(@D))) $(CFLAGS-$(notdir $@))
 cmd_strip     = $(STRIPTOOL) $(STRIP_FLAGS) $^