re-import all libretro code from it's fork

Verbatim copy from https://github.com/libretro/picodrive/ commit
9ae88ef15ff00cacc3877c7ecc13b0092bab50b8 , so look there for the history
of libretro specific changes. Unfortunately there is too much noise and
divergence to merge this in a proper way.

platform/libretro/msvc/msvc-2003-xbox1.bat

@@ -0,0 +1,47 @@
+@SET VSINSTALLDIR=C:\Program Files\Microsoft Visual Studio .NET 2003\Common7\IDE
+@SET VCINSTALLDIR=C:\Program Files\Microsoft Visual Studio .NET 2003
+@SET FrameworkDir=C:\WINDOWS\Microsoft.NET\Framework
+@SET FrameworkVersion=v1.1.4322
+@SET FrameworkSDKDir=C:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1
+@rem Root of Visual Studio common files.
+
+@if "%VSINSTALLDIR%"=="" goto Usage
+@if "%VCINSTALLDIR%"=="" set VCINSTALLDIR=%VSINSTALLDIR%
+
+@rem
+@rem Root of Visual Studio ide installed files.
+@rem
+@set DevEnvDir=%VSINSTALLDIR%
+
+@rem
+@rem Root of Visual C++ installed files.
+@rem
+@set MSVCDir=%VCINSTALLDIR%\VC7
+
+@rem
+@echo Setting environment for using Microsoft Visual Studio .NET 2003 tools.
+@echo (If you have another version of Visual Studio or Visual C++ installed and wish
+@echo to use its tools from the command line, run vcvars32.bat for that version.)
+@rem
+
+@REM %VCINSTALLDIR%\Common7\Tools dir is added only for real setup.
+
+@set PATH=%DevEnvDir%;%MSVCDir%\BIN;%VCINSTALLDIR%\Common7\Tools;%VCINSTALLDIR%\Common7\Tools\bin\prerelease;%VCINSTALLDIR%\Common7\Tools\bin;%FrameworkSDKDir%\bin;%FrameworkDir%\%FrameworkVersion%;%PATH%;
+@set INCLUDE=%MSVCDir%\ATLMFC\INCLUDE;%MSVCDir%\INCLUDE;%FrameworkSDKDir%\include;%INCLUDE%;%XDK%\xbox\include
+@set LIB=%MSVCDir%\ATLMFC\LIB;%MSVCDir%\LIB;%MSVCDir%\PlatformSDK\lib;%XDK%\lib;%XDK%\xbox\lib;%LIB%
+
+@goto end
+
+:Usage
+
+@echo. VSINSTALLDIR variable is not set. 
+@echo.
+@echo SYNTAX: %0
+
+@goto end
+
+:end
+
+devenv /clean Release_LTCG msvc-2003-xbox1.sln
+devenv /build Release_LTCG msvc-2003-xbox1.sln
+exit