obs-d3d11: use sprintf for mingw-w64

We have a sprintf_s function in mingw-w64, but it's the it won't compile
with visual studio because it's the C11 specification (aka the correct
specification that's not made by morons).  Microsoft's version differs
to the specification (and is made by morons), so fall back to sprintf

(note if you can't tell, this commit message was edited by Jim)

libobs-d3d11/d3d11-subsystem.cpp

@@ -142,7 +142,7 @@ void gs_device::InitCompiler()
 	int ver = 49;
 
 	while (ver > 30) {
-		sprintf_s(d3dcompiler, 40, "D3DCompiler_%02d.dll", ver);
+		sprintf(d3dcompiler, "D3DCompiler_%02d.dll", ver);
 
 		HMODULE module = LoadLibraryA(d3dcompiler);
 		if (module) {