Non-MSVC compilers and the SDK

[Gisle Vanem]

I've done some patches to the EveryThing SDK for turning down the warnings etc. from various non-MSVC compilers:

• CygWin - tested with gcc ver. 7.4.0. Both x86 and x64.

• Clang - tested with ver. 8.0.0. Both x86 and x64.

• PellesC - tested with ver. 8.00.170.

• OpenWatcom - tested with ver. 2.0 beta.

Other items I've addressed:

• Allow MSVC to use the fastcall calling convention (option -Gr).
  Therefore a CreateThread() function must be __stdcall (not fastcall).
  Similar for a qsort() function. Ref. MS_CDECL in my diff.

• Ugly part: I needed to make the local hthread variable a public to forcefully terminate
  _Everything_query_thread_proc() (in e.g a SIGINT handler).
  A new function for this would be cleaner.

• Added a Everything_SetLastError(). Ref. the comment for it.

• Allow a static build by testing EVERYTHINGUSERAPI before defining it.

• CygWin is POSIX. Hence no stricmp() and wcsicmp() AFAICS.

• Added some Doxygen tags for my own use in my Envtool program.

I've put my diff-file at my GitHub gist-page.
Using these patches, I've turned down the warnings quite a bit.

David, pick and choose what you like. Again, a million thanks for a truly great program !!

PS. I'm not sure I'm using the last version of the EveryThing SDK.