Add a script to build all dependencies for explicit module build in one
step. This reduces the boiling plate code needed to write a test for
explicit module build and allows the test to be more cross platform and
resilient to module dependencies changes.
Use `resetBenignCodeGenOptions()` from clang dependency scanner to clear
the swift explicit module build cc1 arguments. This fixes the problem
that CurrentWorkingDirectory is leaking through
`-fcoverage-compilation-dir` that can cause extra module variants when
caching is enabled. This also avoid the duplicating the logics for
clearing CodeGen options inside Swift.
rdar://151395300
