The naming convention is different on Windows than on Unix-like
environments. In order to follow the convention we need to substitute
the prefix and the suffix. Take the opportunity to rename the
`target-dylib-extension` to the CMake-like variable
`target-shared-library-suffix` and introduce
`target-shared-library-prefix`. This helps linking the test suite
binaries on Windows.
Actually looking at the dumped IR is usually not interesting, the tests just
need to get to that stage to be able to perform the validation
correctly. Additionally, the IR is very large for some of these tests, so
dumping it makes things sllooooowww when something fails.
