[gjs] arg: Include headers for std::abs()

[Philip Chimento <pchimento src gnome org>]

commit 75e72441221a0416cfa6131a471dcbeac8394e22
Author: Tom Schoonjans <Tom Schoonjans me com>
Date:   Mon Apr 24 22:42:28 2017 -0700

    arg: Include headers for std::abs()
    
    Required for compiling with clang on macOS.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=780350

 gi/arg.cpp |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gi/arg.cpp b/gi/arg.cpp
index 2e33520..81ebf4d 100644
--- a/gi/arg.cpp
+++ b/gi/arg.cpp
@@ -23,6 +23,9 @@
 
 #include <config.h>
 
+#include <cstdlib>
+#include <cmath>
+
 #include "arg.h"
 #include "gtype.h"
 #include "object.h"