Since CMake 3.16, CMake has native precompiled header (PCH) support.
This change swaps Blender's own PCH implementation with the native implementation.
Previously, PCH was only enabled on Windows however,
this new implementation works on all platforms.
For more information see https://cmake.org/cmake/help/latest/command/target_precompile_headers.html
On my system, Linux with ninja running on an i5 8250U
I saw a 60% reduction in compile times for `bf_freestyle` + linking time.
Reviewed By: LazyDodo, brecht
Differential Revision: https://developer.blender.org/D13797
259a71cd3c