Always set the deployment target when building std

[madsmtm]

cc has a bug/feature (I guess depending on how you look at it) where the default deployment target is taken from the SDK instead of from rustc. This causes compiler-builtins to build compiler-rt with the wrong deployment target on iOS.

I've been meaning to change how cc works in this regard, but that's a lengthy process, so let's fix it in bootstrap for now.

The behaviour be seen locally with ./x build library --set build.optimized-compiler-builtins=true for various target triples, and then inspecting with otool -l build/host/stage1/lib/rustlib/*/lib/libcompiler_builtins-*.rlib | rg 'minos|version'. I have added a rmake test that ensures that we now have the same version everywhere.

Fixes #128419
Fixes rust-lang/compiler-builtins#650
See also rust-lang/cargo#13115

@rustbot label O-apple

[rustbot]

r? @Mark-Simulacrum

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[madsmtm]

Okay... So this didn't actually work initially, since bootstrap is for some godforsaken reason calling cc to get default flags, and then later passing passing them to Cargo, which invokes the build script, which calls cc again to get default flags... So all the build flags end up getting duplicated (!), and the values in CFLAGS that were looked up previously end up being prioritized.

I've rebased and fixed that in the first and second commits, but it may break more than I think, so this should probably get a try build before merging.

[rustbot]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

This PR modifies tests/run-make/. If this PR is trying to port a Makefile
run-make test to use rmake.rs, please update the
run-make port tracking issue
so we can track our progress. You can either modify the tracking issue
directly, or you can comment on the tracking issue and link this PR.

cc @jieyouxu

[madsmtm]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

Not sure if I should? It changes in theory (we pass different flags), but in practice it shouldn't (because those flags were already set by cmake-rs, so they were just duplicated)?