This breaking change disambiguates between overriding the lib dir when
performing an installation with the Zig Build System, and overriding the
lib dir that the Zig installation itself uses.
new pipeline `BuildMacOS_arm64`
- `vmImage: 'macOS-10.15' `
new `macos_arm64_script`
- switch from using `make` to `ninja`
- select xcode 12.4
- set zig-cache env variables
- build host-zig binary with xcode, link against llvm for x86_64 (target macos 10.15)
- build arm64-zig binary with xcode and host-zig, link against llvm for arm64 (target macos 11.0)
- ad-hoc codesign arm64 binary with linker
- use host-zig for docgen
- use host-zig for experimental std lib docs
- sync final `release/` hierarchy with `linux_script`
- use gnu-tar for good-practices (set owner, set sort)
enhance `CMakeLists.txt`
- do not build `zig0` when cross-compiling
- disable `BYPRODUCTS` directive `zig1.o` to avoid `ninja` error
see #8265
