+ SEH support for Win32. Enable by cycling with OPT=-dTEST_WIN32_SEH.

Although basic things work (no regressions in test suite, also with TEST_OPT=-O2), there are some secondary issues/TODOs:
- Exception frame around PASCALMAIN is not properly removed in DLLs
- No stack traces yet
- Stack overallocated in finalizer procedures, their entry/exit code needs cleanup
- Signals unit is probably completely broken.


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26225 3ad0048d-3df7-0310-abae-a5850022a9f2