Merge branch 'jk/dev-build-format-security'

Earlier we added "-Wformat-security" to developer builds, assuming
that "-Wall" (which includes "-Wformat" which in turn is required
to use "-Wformat-security") is always in effect.  This is not true
when config.mak.autogen is in use, unfortunately.  This has been
fixed by unconditionally adding "-Wall" to developer builds.

* jk/dev-build-format-security:
  config.mak.dev: add -Wall, primarily for -Wformat, to help autoconf users

Author: gitster

config.mak.dev

@@ -6,6 +6,7 @@ CFLAGS += -pedantic
 # don't warn for each N_ use
 CFLAGS += -DUSE_PARENS_AROUND_GETTEXT_N=0
 endif
+CFLAGS += -Wall
 CFLAGS += -Wdeclaration-after-statement
 CFLAGS += -Wformat-security
 CFLAGS += -Wno-format-zero-length