Fixes 08e7efc76a.
The SM build script worked on its own, but the mac OS libraries script
passes it an unexpected value.
This also fixes cross-compilation arm -> x86.
Harfbuzz is explicitly not used when compiling freetype to avoid
pkgconfig using it.
Reorganize the logic a little bit around architecture handling.
Differential Revision: https://code.wildfiregames.com/D4647
This was SVN commit r26882.
wraitii
f82fc6431b