Disable _FORTIFY_SOURCE to fix Ubuntu build with -Werror

This eliminates the results unused warnings.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

Makefile

@@ -22,6 +22,7 @@ LDFLAGS += $(OS_LDFLAGS) $(ARCH_LDFLAGS)
 
 CPPFLAGS += -I. -I$(SRC_PATH) -MMD -MP -MT $@
 CPPFLAGS += -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
+CPPFLAGS += -U_FORTIFY_SOURCE
 LIBS=
 ifdef CONFIG_STATIC
 LDFLAGS += -static

Makefile.target

@@ -111,6 +111,7 @@ CFLAGS+=$(OS_CFLAGS) $(ARCH_CFLAGS)
 LDFLAGS+=$(OS_LDFLAGS) $(ARCH_LDFLAGS)
 
 CPPFLAGS+=-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
+CPPFLAGS+=-U_FORTIFY_SOURCE
 LIBS+=-lm
 ifdef CONFIG_WIN32
 LIBS+=-lwinmm -lws2_32 -liphlpapi