configure.ac: Enable -Wall flag

Change-Id: Ib05f7862081708d578d8f0302d926aab42897dc2
diff --git a/configure.ac b/configure.ac
index 2b8974f..dd1d75e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -58,6 +58,9 @@
 	CPPFLAGS="$CPPFLAGS -fsanitize=address -fsanitize=undefined"
 fi
 
+CFLAGS="$CFLAGS -Wall"
+CPPFLAGS="$CPPFLAGS -Wall"
+
 AC_OUTPUT(
 	libosmo-ranap.pc
 	src/Makefile