llvm4: unconditionally set triples, not just on musl.

[dtzWill]

Split off from #42454 as requested.

Boxes I've checked below aren't actually for this exact commit,
but the original I sent to master and actually the one I tested on
a slightly older master before moving to staging.
Basically these really should apply but who can say :).

Build in-flight anyway :).

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

---

[dtzWill]

@GrahamcOfBorg build tests.cc-wrapper-libcxx-4 tests.cc-wrapper-clang-4

[GrahamcOfBorg]

Failure on x86_64-darwin (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

-- Configuring incomplete, errors occurred!
See also "/tmp/nix-build-llvm-4.0.1.drv-0/llvm/build/CMakeFiles/CMakeOutput.log".
See also "/tmp/nix-build-llvm-4.0.1.drv-0/llvm/build/CMakeFiles/CMakeError.log".
builder for '/nix/store/3kpdhxrwp51z0v0p7pkjy1q1sw8dghrq-llvm-4.0.1.drv' failed with exit code 1
cannot build derivation '/nix/store/289q198div0fy3z052pg7a9dwxr2p9ab-clang-4.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/qm8g588yi1pzy5nd4caad8lg380wjy07-clang-manpages-4.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/i2zmpbn1gsi47dhysfmkslyg8kahic02-clang-wrapper-4.0.1.drv': 2 dependencies couldn't be built
cannot build derivation '/nix/store/lrvx0qy6f4lrpm6zbisl8amfnh94v674-stdenv-darwin.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/xh5p84p4gaz09p3hzn1ak1rgg9b1mr68-cc-wrapper-test.drv': 1 dependencies couldn't be built
�[31;1merror:�[0m build of '/nix/store/xh5p84p4gaz09p3hzn1ak1rgg9b1mr68-cc-wrapper-test.drv' failed

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

checking whether compiler builds valid C binaries... ok
checking whether compiler builds valid C binaries... ok
checking whether compiler builds valid C++ binaries... ok
checking whether compiler uses NIX_CFLAGS_COMPILE... ok
checking whether compiler uses NIX_LDFLAGS... ok
checking whether compiler builds valid C++ binaries... ok
checking whether compiler uses NIX_CFLAGS_COMPILE... ok
checking whether compiler uses NIX_LDFLAGS... ok
/nix/store/332ym6qw5m16chkpk2gshwjq85bk39gb-cc-wrapper-test
/nix/store/6mkzrlgq9bipvixx3p6q4k5p4ibqmcxj-cc-wrapper-test

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

Selected multilib: .;@m64
checking whether compiler builds valid C binaries... ok
checking whether compiler builds valid C++ binaries... ok
checking whether compiler uses NIX_CFLAGS_COMPILE... ok
checking whether compiler builds valid C++ binaries... ok
checking whether compiler uses NIX_CFLAGS_COMPILE... ok
checking whether compiler uses NIX_LDFLAGS... ok
checking whether compiler uses NIX_LDFLAGS... ok
/nix/store/3qwxpf6x2pjxqf35d576zdy0f1vky4jk-cc-wrapper-test
/nix/store/944lp1msyv4fhxqvsbw3njkgqv1ynn07-cc-wrapper-test

[dtzWill]

@GrahamcOfBorg build tests.cc-wrapper-libcxx-4 tests.cc-wrapper-clang-4

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

/nix/store/3qwxpf6x2pjxqf35d576zdy0f1vky4jk-cc-wrapper-test
/nix/store/944lp1msyv4fhxqvsbw3njkgqv1ynn07-cc-wrapper-test

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

/nix/store/332ym6qw5m16chkpk2gshwjq85bk39gb-cc-wrapper-test
/nix/store/6mkzrlgq9bipvixx3p6q4k5p4ibqmcxj-cc-wrapper-test

[GrahamcOfBorg]

Failure on x86_64-darwin (full log)

Attempted: tests.cc-wrapper-libcxx-4, tests.cc-wrapper-clang-4

Partial log (click to expand)

[ 22%] Building CXX object lib/Analysis/CMakeFiles/LLVMAnalysis.dir/Analysis.cpp.o
[ 22%] Building CXX object lib/Analysis/CMakeFiles/LLVMAnalysis.dir/AssumptionCache.cpp.o
[ 22%] Building CXX object lib/Analysis/CMakeFiles/LLVMAnalysis.dir/BasicAliasAnalysis.cpp.o
building of '/nix/store/3kpdhxrwp51z0v0p7pkjy1q1sw8dghrq-llvm-4.0.1.drv' timed out after 1800 seconds
cannot build derivation '/nix/store/289q198div0fy3z052pg7a9dwxr2p9ab-clang-4.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/qm8g588yi1pzy5nd4caad8lg380wjy07-clang-manpages-4.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/i2zmpbn1gsi47dhysfmkslyg8kahic02-clang-wrapper-4.0.1.drv': 2 dependencies couldn't be built
cannot build derivation '/nix/store/lrvx0qy6f4lrpm6zbisl8amfnh94v674-stdenv-darwin.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/xh5p84p4gaz09p3hzn1ak1rgg9b1mr68-cc-wrapper-test.drv': 1 dependencies couldn't be built
�[31;1merror:�[0m build of '/nix/store/xh5p84p4gaz09p3hzn1ak1rgg9b1mr68-cc-wrapper-test.drv' failed

[dtzWill]

Well seems to have worked for llvm 3.8, 3.9--or at least no obvious fires were started as a result :).

Darwin looks good: https://hydra.nixos.org/build/76526688 (might not be first build containing change, but look at log to see we're setting triples as expected and such).

Let's try 4!