The recommendation from engineers within Microsoft is that libraries
should have a calling convention specified in the public API, and that
calling convention should be cdecl unless there are strong reasons to
use a different calling convention.

We previously offered end-users the choice between cdecl and stdcall
calling conventions.  We did this for presumed wider compatibility: most
Windows applications will use cdecl, but C# and PInvoke default to
stdcall for WINAPI compatibility.  (On Windows, the standard library
functions are are stdcall so PInvoke also defaults to stdcall.)

However, C# and PInvoke can easily call cdecl APIs by specifying an
annotation.

Thus, we will explicitly declare ourselves cdecl and remove the option
to build as stdcall.