Add compilation symbol to preserve DllExport attribute (metadata)

[OmegaExtern]

Reference to DllExport is always removed, which may be unwanted in some situations.

What I would suggest to do is:
Search compilation symbols for DLLEXPORT_PRESERVE, and if it is present, do not remove reference to DllExport, otherwise keep current behavior.

[3F]

which may be unwanted in some situations

for example ? :)

[OmegaExtern]

for example ? :)

I don't have any good example where metadata should be preserved, anyway up to you.. It is not hard to do.