[librsvg: 1/2] Add docs for installing dependencies and build on macOS

[Federico Mena Quintero <federico src gnome org>]

commit f8170003ac7bf80e7165b55369e974658f5dde38
Author: Brion Vibber <brion pobox com>
Date:   Sun Feb 25 21:37:41 2018 -0800

    Add docs for installing dependencies and build on macOS
    
    Updates COMPILING.md with macOS setup instructions.
    
    Deps from Homebrew are mostly straightforward, but there are
    a couple oddities due to interaction between system packages
    and the Homebrew packages.
    
    Fixes https://gitlab.gnome.org/GNOME/librsvg/issues/209

 COMPILING.md | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
---
diff --git a/COMPILING.md b/COMPILING.md
index a755b2ba..d8fd1226 100644
--- a/COMPILING.md
+++ b/COMPILING.md
@@ -100,6 +100,33 @@ libxml2-devel libcroco-devel cairo-devel \
 pango-devel gdk-pixbuf-devel
 ```
 
+### macOS systems
+
+Dependencies may be installed using [Homebrew](https://brew.sh) or another
+package manager.
+
+```sh
+brew install cairo gdk-pixbuf glib libcroco pango \
+gobject-introspection rust
+
+export PKG_CONFIG_PATH="`brew --prefix`/lib/pkgconfig:\
+`brew --prefix libffi`/lib/pkgconfig:\
+/usr/lib/pkgconfig"
+export ARCHFLAGS="-arch x86_64"
+```
+
+Note that `PKG_CONFIG_PATH` must be manually set to include Homebrew's libffi,
+as the system libffi is too old but Homebrew does not install it in a public
+location by default.
+
+Currently, cairo 1.15.4 or later must also be installed manually, as the
+Homebrew package is for the older stable release. This may require adding
+it to `PKG_CONFIG_PATH` as well if you do not install it in `/usr/local`.
+
+Setting `ARCHFLAGS` is required if gobject-introspection is using the system
+Python provided by Apple, as on Homebrew.
+
+
 # Basic compilation instructions
 
 If you are compiling a tarball: