This commit adds -sil-output-path and -ir-output-path frontend options that
allow generating SIL and LLVM IR files as supplementary outputs during normal
compilation.
These options can be useful for debugging and analysis tools
workflows that need access to intermediate compilation artifacts
without requiring separate compiler invocations.
Expected behaviour:
Primary File mode:
- SIL: Generates one .sil file per source file
- IR: Generates one .ll file per source file
Single-threaded WMO mode:
- SIL: Generates one .sil file for the entire module
- IR: Generates one .ll file for the entire module
Multi-threaded WMO mode:
- SIL: Generates one .sil file for the entire module
- IR: Generates separate .ll files per source file
File Maps with WMO:
- Both SIL and IR outputs using first entry's naming, which is
consistent with the behaviour of other supplementary outputs.
rdar://160297898
