[PATCH] Disable AVX instruction set on IA32 and x86_64 platforms

If gnu-efi is compiled with "-march=native" on a host that supports AVX, both
gcc and clang will use AVX instructions freely which is currently not supported
and will result in a non-functional gnu-efi build (e.g. black screen, hangs).

For now, disable AVX on IA32 and x86_64 by checking first if the compiler does
actually support the appropriate flag (-mno-avx) and use it if possible.

Credit for the compiler command line to check if a flag is supported goes to
Gentoo's awesome flag-o-matic eclass, where it is taken from. Thanks.

Signed-off-by: Matthias Dahl <matthias.dahl@binary-island.eu>
Signed-off-by: Nigel Croxon <ncroxon@redhat.com>

Make.defaults

@@ -120,6 +120,14 @@ ifeq ($(ARCH),x86_64)
   endif
 endif
 
+ifneq (,$(filter $(ARCH),ia32 x86_64))
+  # Disable AVX, if the compiler supports that.
+  CC_CAN_DISABLE_AVX=$(shell $(CC) -Werror -c -o /dev/null -xc -mno-avx - </dev/null >/dev/null 2>&1 && echo 1)
+  ifeq ($(CC_CAN_DISABLE_AVX), 1)
+    CFLAGS += -mno-avx
+  endif
+endif
+
 ifeq ($(ARCH),mips64el)
   CFLAGS += -march=mips64r2
   ARCH3264 = -mabi=64