[gnome-terminal] build: Add new warning flag

[Christian Persch <chpe src gnome org>]

commit 82ba2c08eb80ab6e87ff7e0df7257d08e8b52466
Author: Christian Persch <chpe gnome org>
Date:   Sat Feb 14 22:48:02 2015 +0100

    build: Add new warning flag

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 5180ec6..7f9f16a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -299,6 +299,7 @@ CC_CHECK_FLAGS_APPEND([WARN_CFLAGS],[CFLAGS],[ \
   -Wuninitialized \
   -Wunsafe-loop-optimizations \
   -Wwrite-strings \
+  -Wformat-signedness \
   -fno-common \
   -fdiagnostics-show-option \
   -fno-strict-aliasing \