[CMake] CMake --debug-trycompile option breaking tests

[Clifford Yapp]

Hmm.  What about changing that option to make one sub-directory per
test instead of doing each one in the same temp directory?  Or if
try_compile doesn't support that, moving the generated files to a
subdirectory after the try_compile proper has run?  That would allow
"normal" cmake building while still preserving the files - it's rather
unexpected behavior to have it do what it does now.  Is there a reason
not to have one directory per test in a "try_compile" subdirectory?

Cheers,
CY