utils: enable SPM self-hosted test suite on Windows

This will enable the SPM test suite to be built with a self-hosted
build to ensure that we do not regress the SPM builds on Windows.

Author: compnerd

utils/build-windows-toolchain.bat

@@ -60,7 +60,7 @@ set TMPDIR=%BuildRoot%\tmp
 set NINJA_STATUS=[%%f/%%t][%%p][%%es] 
 
 :: Build the -Test argument, if any, by subtracting skipped tests
-set TestArg=-Test swift,dispatch,xctest,
+set TestArg=-Test swift,dispatch,xctest,swiftpm,
 for %%I in (%SKIP_TESTS%) do (call set TestArg=%%TestArg:%%I,=%%)
 if "%TestArg:~-1%"=="," (set TestArg=%TestArg:~0,-1%) else (set TestArg= )