[PATCH v4 3/4] Makefile: add a DEVOPTS to suppress -Werror under DEVELOPER

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Add a DEVOPTS variable that'll be used to tweak the behavior of
DEVELOPER.

I've long wanted to use DEVELOPER=1 in my production builds, but on
some old systems I still get warnings, and thus the build would
fail. However if the build/tests fail for some other reason, it would
still be useful to scroll up and see what the relevant code is warning
about.

This change allows for that. Now setting DEVELOPER will set -Werror as
before, but if DEVOPTS=no-error is provided is set you'll get the same
warnings, but without -Werror.

Helped-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile       | 10 ++++++++++
 config.mak.dev |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/Makefile b/Makefile
index 3038c78325..9a57495fae 100644
--- a/Makefile
+++ b/Makefile
@@ -445,6 +445,16 @@ all::
 # Define DEVELOPER to enable more compiler warnings. Compiler version
 # and family are auto detected, but could be overridden by defining
 # COMPILER_FEATURES (see config.mak.dev)
+#
+# When DEVELOPER is set, DEVOPTS can be used to control compiler
+# options.  This variable contains keywords separated by
+# whitespace. The following keywords are are recognized:
+#
+#    no-error:
+#
+#        suppresses the -Werror that implicitly comes with
+#        DEVELOPER=1. Useful for getting the full set of errors
+#        without immediately dying, or for logging them.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
diff --git a/config.mak.dev b/config.mak.dev
index 716a14ecc7..7a54426d78 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -1,4 +1,6 @@
+ifeq ($(filter no-error,$(DEVOPTS)),)
 CFLAGS += -Werror
+endif
 CFLAGS += -Wdeclaration-after-statement
 CFLAGS += -Wno-format-zero-length
 CFLAGS += -Wold-style-definition
-- 
2.17.0.290.gded63e768a