[OS-BUILD PATCHv2] makefile: Add -Werror support for RHEL

[Prarit Bhargava (via Email Bridge)]

From: Prarit Bhargava

makefile: Add -Werror support for RHEL

The -Werror flag should be enabled for RHEL.  In ARK, however, it is a bit
tricky to enable -Werror as a build bug occasionally leaks through
upstream review and into Linus' tree.  As a consequence, CONFIG_WERROR
cannot be enabled in ARK but the code to add the flag for RHEL commpiles
can be added to the top-level makefile.

This code could be placed in the top-level Makefile, around the -Werror
line added by Linus in 3fe617ccafd6 ("Enable '-Werror' by default for all
kernel builds"), but given the amount of RHEL Only code here it is best to
keep it separated in our top-level makefile.  Reviewers should note that
there is no harm in calling 'KBUILD_CFLAGS += -Werror' twice and that
-Werror only appears once in gcc calls when compiling kernel files.

Signed-off-by: Prarit Bhargava

diff --git a/makefile b/makefile
index blahblah..blahblah 100644
--- a/makefile
+++ b/makefile
@@ -14,3 +14,13 @@ dist-%::
 distg-%::
    $(MAKE) -C redhat $(@) $(_EXTRA_ARGS)

+# Enable -Werror for RHEL
+ifneq ($(DISABLE_WERROR),1)
+ifneq ($(WITH_GCOV),1)
+ifeq ($(KBUILD_EXTMOD),)
+ifneq (,$(filter $(ARCH), x86 x86_64 powerpc s390 aarch64))
+KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
+endif
+endif
+endif
+endif

--
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2240

[Prarit Bhargava (via Email Bridge)]

From: Prarit Bhargava on gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2240#note_1230134...

Good point, however, as I mentioned in the commit log we still occasionally
see compile warnings in upstream code and we cannot have the build fail in
ARK/Fedora due to those errors.  That would bring ARK/Fedora to a halt :(.  As
such, I am not enabling CONFIG_WERROR in ARK/Fedora.

As for the top-level Makefile, I also addressed in the commit log: there is
enough RHEL only code here that I'd prefer not to put it in the top-level
Makefile as doing so would make future rebases in ARK/Fedora more difficult
for @ptalbert and @jmflinuxtx.  That's why I've put the code in out top-level
makefile instead of the Makefile.

@ptalbert and @jmflinuxtx?  Thoughts?  Am I overthinking this and maybe I
should just put the code in the top-level Makefile?