Deal with clang-cl doing the sane (but different to MSVC) thing, of
generating an empty import library, rather than silently ignoring
/IMPLIB when there are no exports.
It's a (presumably unintentional) quirk of the current implementation of
SharedLibrary.determine_filenames() that if both name_suffix and
name_prefix are set, an import library isn't generated.
Adjust test 'common/25 library versions': Make the library have exports,
so an implib is generated with MSVC. Add implib to set of files expected
to be installed
Adjust test 'common/122 shared module': Add libnosyms implib to set of
files expected to be installed, except for MSVC, where none is generated
as it has no exports
Shared modules may be resource-only DLLs, or might automatically
self-initialize using C constructors or WinMain at DLL load time.
When an import library is not found for a shared module, just print
a message about it instead of erroring out.
Fixes#3965
Jussi Pakkanen
Jon Turney
Marco Trevisan (Treviño)
Nirbheek Chauhan