Very long macOS build times

[NiklasEi]

See the build times on GitHub actions:

[NiklasEi]

It looks like the build step gets stuck between downloading dependencies and compiling them. The compile times themselves look normal.

2021-04-01T16:12:25.0569480Z   Downloaded ahash v0.7.2
2021-04-01T16:12:25.0672550Z   Downloaded cc v1.0.67
2021-04-01T16:12:25.0760620Z   Downloaded Inflector v0.11.4
2021-04-01T16:12:25.0898820Z   Downloaded async-executor v1.4.0
2021-04-01T18:31:08.0192370Z    Compiling libc v0.2.91
2021-04-01T18:31:08.0199130Z    Compiling proc-macro2 v1.0.24
2021-04-01T18:31:08.0200050Z    Compiling unicode-xid v0.2.1
2021-04-01T18:31:08.8948470Z    Completed unicode-xid v0.2.1 in 0.9s
2021-04-01T18:31:08.8949060Z    Compiling syn v1.0.65
2021-04-01T18:31:17.0937290Z    Completed libc v0.2.91 custom-build in 9.1s
2021-04-01T18:31:17.0947910Z    Completed syn v1.0.65 custom-build in 8.2s
2021-04-01T18:31:17.0956210Z    Compiling bitflags v1.2.1

[NiklasEi]

The long macOS build times seem to be caused by the fact that I have a build script. The build finishes in ~10min without build.rs but takes up to several hours with an empty build script. Since there doesn't seem to be a way of defining a build script only for specific targets jet (rust-lang/cargo#4932), I'm kind of stuck with this issue.

[NiklasEi]

To finally have reasonable macOS build times I am now deleting build.rs in a pre-build step of the macOS job (see 6ad9e81). Thanks, @mockersf for the idea.