In some internal configurations we set the
`SWIFT_LOADED_MODULE_TRACE_FILE` environment variable when running the
build of the compiler -- as a result, this causes `-parse` to always
fails, preventing to detect properly if we can use `disable-implicit*`
flags.
Addresses rdar://115338219
For compiling codes required for macro support, we now need swiftc
compiler in the build machine.
Unlike Darwin OSes, where swiftCore runtime is guaranteed to be present
in /usr/lib, Linux doesn't have ABI stability and the stdlib of the
build machine is not at the specific location. So the built compiler
cannot relies on the shared object in the toolchain.
swift_supports_implicit_module invokes /path/to/toolchain/usr/bin/swiftc
directly without using `xcrun`. That fails to set necessary
environmental variables to make swiftc infer the SDK path. Because of
that swift_supports_implicit_module used to fail because the test
compilation fails to load the stdlib. This PR workaround it by passing
`-parse-stdlib` to avoid implicit stdlib loading.
Once the API has gone through Swift Evolution, we will want to implicitly
import the _Backtracing module. Add code to do that, but set it to off
by default for now.
rdar://105394140
