[gnome-common] compiler-warnings: Add -Werror=return-type

[Ting-Wei Lan <lantw src gnome org>]

commit 334bb90c5bcf96105aed8eac464bb296bf1aa9c9
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Mon Dec 15 23:22:15 2014 +0800

    compiler-warnings: Add -Werror=return-type
    
    Function return type mismatch should be considered broken, as it can cause
    unexpected result or compilation error.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=741558

 macros2/gnome-compiler-flags.m4 |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/macros2/gnome-compiler-flags.m4 b/macros2/gnome-compiler-flags.m4
index 2261949..ec2d896 100644
--- a/macros2/gnome-compiler-flags.m4
+++ b/macros2/gnome-compiler-flags.m4
@@ -1,6 +1,6 @@
 # gnome-compiler-flags.m4
 #
-# serial 2
+# serial 3
 #
 
 dnl GNOME_COMPILE_WARNINGS
@@ -49,6 +49,7 @@ AC_DEFUN([GNOME_COMPILE_WARNINGS],[
         -Werror=format-security \
         -Werror=format=2 \
         -Werror=missing-include-dirs \
+        -Werror=return-type \
     "
 
     dnl Additional warning or error flags provided by the module author to