CI accidentally skips over crux-llvm tests on macOS

[RyanGlScott]

Recently, I came to wonder why the macOS CI jobs weren't catching #885, which should prevent the crux-llvm tests from passing on macOS. It turns out this is because the CI isn't actually running the crux-llvm test suite on macOS at all! Take a look at what happens on a typical macOS job like this one:

+ /Users/runner/work/crucible/crucible/llvm/bin/clang-withIncl --version
clang-11: error: no input files
+ echo clang version unknown
clang version unknown
+ /Users/runner/work/crucible/crucible/llvm/bin/llvm-link --version
LLVM (http://llvm.org/):
+ cabal v2-test crux-llvm
  LLVM version 11.0.0
  Optimized build.
  Default target: x86_64-apple-darwin19.6.0
  Host CPU: ivybridge
Build profile: -w ghc-9.2.2 -O1
In order, the following will be built (use -v for more details):
 - crux-llvm-0.6.0.99 (test:crux-llvm-test) (first run)
<snip>
Running 1 test suites...
Test suite crux-llvm-test: RUNNING...
Test suite crux-llvm-test: PASS
Test suite logged to:
/Users/runner/work/crucible/crucible/dist-newstyle/build/x86_64-osx/ghc-9.2.2/crux-llvm-0.6.0.99/t/crux-llvm-test/test/crux-llvm-0.6.0.99-crux-llvm-test.log
1 of 1 test suites (1 of 1 test cases) passed.

The first suspicious thing here is that the whole test suite takes 12 seconds to run, which is far too short. The second suspicious thing is that clang-withIncl --version prints clang-11: error: no input files instead of the version number. This is a consequence of how the CI is setting up clang on macOS. It assembles a wrapper script named clang-withIncl here:

crucible/.github/workflows/crux-llvm-build.yml

Lines 173 to 174 in 4158b6f

	echo "#!/usr/bin/env bash" > llvm/bin/clang-withIncl
	echo "clang -I${{ github.workspace }}/llvm/include -I${{ github.workspace }}/llvm/include/c++/v1" >> llvm/bin/clang-withIncl

There's a mistake here, however: the invocation of clang doesn't pass through the arguments (e.g., with ${1+"$@"}), so no matter what arguments you pass to the clang-withIncl script, it will simply invoke clang with no input files. We should change this script so that it plumbs through the arguments.