Also add a new capability for ModuleDescriptor, which is used to obtain the
platform in the multi-platform scenario in tests.
Suppress the following errors for platform functions: "function has no body"
and "nothing to inline". Also do not report redeclaration between platform and
non-platform functions because this is the case when the common +
platform-specific code are analyzed together.
Note that some diagnostics reported in tests are not yet implemented in this
commit, they appear in subsequent commits
Alexander Udalov