build: adjust compile.h compiler version command line

CFLAGS is just from Config.mk, drop its use. Don't even bother to
instead use the flags used to build Xen.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/build.mk

@@ -23,7 +23,7 @@ define cmd_compile.h
 	    -e 's/@@whoami@@/$(XEN_WHOAMI)/g' \
 	    -e 's/@@domain@@/$(XEN_DOMAIN)/g' \
 	    -e 's/@@hostname@@/$(XEN_BUILD_HOST)/g' \
-	    -e 's!@@compiler@@!$(shell $(CC) $(CFLAGS) --version 2>&1 | head -1)!g' \
+	    -e 's!@@compiler@@!$(shell $(CC) --version 2>&1 | head -1)!g' \
 	    -e 's/@@version@@/$(XEN_VERSION)/g' \
 	    -e 's/@@subversion@@/$(XEN_SUBVERSION)/g' \
 	    -e 's/@@extraversion@@/$(XEN_EXTRAVERSION)/g' \