[btls] Fixes for windows. (#8653)
* [btls] Do not give gcc flags to msvc.
* [btls] #include "btls-foo.h" instead of #include <btls-foo.h> to work
with existing build system, on Windows, with out-of-tree build.
Not sure which factor does not like <> but "" should be ok.
* [blts] MONO_API is not used consistently and therefore errors on Windows.
1. Make it be nothing.
1b. Use a .def file if there are actual exports.
Really, .def files are a good idea.
or
2. Use it consistently.
This does #1.
34 files changed: