ANGLE PKGBUILD with custom patches for building under Arch Linux. Used in RVGL.

• Based on the chromium/3497 branch (Chrome 69).
• Build optimized i686 and x86_64 release libs.
• Windows XP support.
• Undecorated export functions and static std libs for wider compatibility.
• Requires mingw-w64-headers >= 6.0.0.