[gucharmap] build: Update warning flags

[Christian Persch <chpe src gnome org>]

commit a5346ddd5502ff7e6be39c7ea0686545b03cc062
Author: Christian Persch <chpe gnome org>
Date:   Tue Mar 3 19:32:19 2015 +0100

    build: Update warning flags

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 1e825d7..76fe1eb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -231,6 +231,7 @@ CC_CHECK_CFLAGS_APPEND([ \
   -Wstrict-aliasing=2 -Winit-self -Wunsafe-loop-optimizations \
   -Wdeclaration-after-statement -Wold-style-definition \
   -Wno-missing-field-initializers -Wno-unused-parameter \
+  -Wformat-signedness \
   -fno-common -Wno-switch-enum])
 
 # ********