Add the Clang specific -Wmissing-variable-declarations to WARNS=6.

This compiler flag enforces that that people either mark variables
static or use an external declarations for the variable, similar to how
-Wmissing-prototypes works for functions.

Due to the fact that Yacc/Lex generate code that cannot trivially be
changed to not warn because of this (lots of yy* variables), add a
NO_WMISSING_VARIABLE_DECLARATIONS that can be used to turn off this
specific compiler warning.

Announced on:	toolchain@

1 files changed, 2 insertions, 0 deletions

diff --git a/bin/expr/Makefile b/bin/expr/Makefile
index 544853e10a25..b86cf6686ab0 100644
--- a/bin/expr/Makefile
+++ b/bin/expr/Makefile
@@ -4,4 +4,6 @@ PROG=	expr
 SRCS=	expr.y
 YFLAGS=
 
+NO_WMISSING_VARIABLE_DECLARATIONS=
+
 .include <bsd.prog.mk>