Fix cross-compiling zig on alpine

[Electroid]

What does this PR do?

The ordering of options in CMake is important. Before project() is called, variables such as LINUX and WIN32 correspond to the host platform, but after project() is called, it corresponds to the target platform.

• Globals.cmake is evaluated before project()
• Options.cmake is evaluated after project()

Previously, ABI was calculated in Globals, but this would mean that if you tried to cross-compile Zig on an Alpine host, it would think that the target should also have the musl ABI.

[robobun]

❌ @Electroid, your commit 290588d has some failures in #6807