[gtksourceview] build: disable -Werror by default

[Sébastien Wilmet <swilmet src gnome org>]

commit baa09c0349338dafbb4b178e9d5f818e37cde550
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Mon Apr 3 07:23:23 2017 +0200

    build: disable -Werror by default
    
    See this thread:
    https://mail.gnome.org/archives/desktop-devel-list/2017-April/msg00000.html
    
    -Werror was anyway already disabled by default in Jhbuild.

 configure.ac |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 890b00c..5a4407f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -94,9 +94,10 @@ AC_PATH_PROG(GLIB_MKENUMS, glib-mkenums)
 AC_PATH_PROG(GLIB_COMPILE_RESOURCES, glib-compile-resources)
 AC_PATH_PROG(ITSTOOL, itstool)
 
-# Compile warnings
+# Compile warnings. There can be deprecation warnings at any time, so disable
+# -Werror by default with the [yes] argument.
 AX_REQUIRE_DEFINED([AX_COMPILER_FLAGS])
-AX_COMPILER_FLAGS([WARN_CFLAGS], [WARN_LDFLAGS])
+AX_COMPILER_FLAGS([WARN_CFLAGS], [WARN_LDFLAGS], [yes])
 
 AC_ARG_ENABLE(deprecations,
               [AS_HELP_STRING([--disable-deprecations],