Document macOS build requirements in COMPILING.md
There are a couple oddities building on macOS (tested on 10.13.3 with Xcode 9.2); I'll write up a pull request for
COMPILING.md in a bit.
- add instructions on getting dependencies from eg homebrew
- note cairo 1.15.4+ must be installed manually for now (unstable, so not packaged)
- tries to use ELF-specific
-Bsymbolic-functionsoption? must manually pass
--disable-Bsymbolicto configure (can we auto-detect this?)
- system libffi has no .pc file, which causes the check for gobject-introspection to fail; if using homebrew's libffi must add it to
PKG_CONFIG_PATHmanually or use '
brew link' which may be mysterious
- cargo's compilation of the bindings seems to be either i386 or dual-arch x86_64+i386 which dies in glib's long long size check -- running as
ARCHFLAGS="-arch x86_64" makeforces a 64-bit only build (which is what we want anyway)