[PATCH v2 2/5] Makefile: add -fno-builtin-bcmp

[Nick Desaulniers]

The issue with using `-fno-builtin-*` flags was that they were not
retained during an LTO link with LLVM.  This was fixed in clang-11 by
https://reviews.llvm.org/D71193
(0508c994f0b14144041f2cfd3ba9f9a80f03de08), which is also the minimum
supported version of clang for LTO.  Use `-fno-builtin-bcmp` instead.

With this applid, we can cleanly revert
commit 5f074f3e192f ("lib/string.c: implement a basic bcmp")

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index e523dc8d30e0..def590b743a9 100644
--- a/Makefile
+++ b/Makefile
@@ -579,6 +579,7 @@ CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
 CLANG_FLAGS	+= -fno-builtin-stpcpy
+CLANG_FLAGS	+= -fno-builtin-bcmp
 KBUILD_CFLAGS	+= $(CLANG_FLAGS)
 KBUILD_AFLAGS	+= $(CLANG_FLAGS)
 export CLANG_FLAGS
-- 
2.28.0.297.g1956fa8f8d-goog