Improve MinGW-w64 compatibility on 64-bit Windows.

- try to disable generation of calls to ___chkstk_ms when compiling with
msvc
- allow specifying dependency of scipy extensions to system libraries
(like gfortran and mingwex) without imposing them to all libraries (e.g.
by returning these names from Gnu95FCompiler.get_libraries());

Revert "mingw64 compatibility"

This reverts commit c60b680ad8a2e26ae9878817614b986956acf86b.

always link to gfortran dll

also disable stack checks that require linking to the gcc runtime