Bug 1380114 Update OpenVR to build with MinGW r=kip

This involved four commits:
- Windows.h -> windows.h and similar https://github.com/ValveSoftware/openvr/pull/508
- Add a void* cast for a farproc auto-conversion https://github.com/ValveSoftware/openvr/pull/509
- Add share.h https://github.com/ValveSoftware/openvr/pull/510
- Use GCC Variadic Macros https://github.com/ValveSoftware/openvr/pull/511

This is a reapply of Bug 1363173. Hopefully Valve will actually include the patches in the next release.

MozReview-Commit-ID: KC7Z3r8qSUY

--HG--
extra : rebase_source : 7c712bf64cfedd9d895083f8f3111b41850c30ff

gfx/vr/openvr/src/envvartools_public.cpp

@@ -3,7 +3,7 @@
 #include <stdlib.h>
 
 #if defined(_WIN32)
-#include <Windows.h>
+#include <windows.h>
 
 #undef GetEnvironmentVariable
 #undef SetEnvironmentVariable

gfx/vr/openvr/src/pathtools_public.cpp

@@ -3,11 +3,12 @@
 #include "pathtools_public.h"
 
 #if defined( _WIN32)
-#include <Windows.h>
+#include <windows.h>
 #include <direct.h>
-#include <Shobjidl.h>
-#include <KnownFolders.h>
-#include <Shlobj.h>
+#include <shobjidl.h>
+#include <knownfolders.h>
+#include <shlobj.h>
+#include <share.h>
 
 #undef GetEnvironmentVariable
 #else

gfx/vr/openvr/src/sharedlibtools_public.cpp

@@ -3,7 +3,7 @@
 #include <string.h>
 
 #if defined(_WIN32)
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 #if defined(POSIX)
@@ -22,7 +22,7 @@ SharedLibHandle SharedLib_Load( const char *pchPath )
 void *SharedLib_GetFunction( SharedLibHandle lib, const char *pchFunctionName)
 {
 #if defined( _WIN32)
-	return GetProcAddress( (HMODULE)lib, pchFunctionName );
+  return (void*)GetProcAddress( (HMODULE)lib, pchFunctionName );
 #elif defined(POSIX)
 	return dlsym( lib, pchFunctionName );
 #endif

gfx/vr/openvr/src/vrpathregistry_public.cpp

@@ -9,7 +9,7 @@
 
 #if defined( WIN32 )
 #include <windows.h>
-#include <Shlobj.h>
+#include <shlobj.h>
 
 #undef GetEnvironmentVariable
 #elif defined OSX
@@ -23,7 +23,9 @@
 #include <algorithm>
 
 #ifndef VRLog
-	#if defined( WIN32 )
+	#if defined( __MINGW32__ )
+		#define VRLog(args...)		fprintf(stderr, args)
+	#elif defined( WIN32 )
 		#define VRLog(fmt, ...)		fprintf(stderr, fmt, __VA_ARGS__)
 	#else
 		#define VRLog(args...)		fprintf(stderr, args)