[folks] build: Enable colourised output from GCC

[Philip Withnall <pwithnall src gnome org>]

commit 18c629cf1d40a72c5f9f04a31dbdf4a265306cd9
Author: Philip Withnall <philip withnall collabora co uk>
Date:   Fri Oct 25 18:09:50 2013 +0100

    build: Enable colourised output from GCC
    
    If GCC supports it, enable the -fdiagnostics-color=auto option, which adds
    colour to warnings and errors outputted by GCC. Enable this for both generated
    and non-generated C code.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=710869

 configure.ac |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 7b45499..991a94e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -504,6 +504,10 @@ FOLKS_ADD_WARNING([ERROR_CFLAGS], [old-style-declaration])
 FOLKS_ADD_WARNING([ERROR_CFLAGS], [old-style-definition])
 FOLKS_ADD_WARNING([ERROR_CFLAGS], [strict-prototypes])
 
+# Enable colourised compiler output.
+AS_COMPILER_FLAG([-fdiagnostics-color=auto],
+                 [ERROR_CFLAGS="$ERROR_CFLAGS -fdiagnostics-color=auto"])
+
 AS_COMPILER_FLAG([-Wall], [C_ERROR_CFLAGS="-Wall"], [C_ERROR_CFLAGS=""])
 AS_COMPILER_FLAG([-Werror], [werror=yes], [werror=no])