Fix build -alltargets on Windows (#85039)

Author: markples

src/tests/build.cmd

@@ -111,7 +111,7 @@ if /i "%arg%" == "composite"             (set __CompositeBuildMode=1&set __TestB
 if /i "%arg%" == "pdb"                   (set __CreatePdb=1&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
 if /i "%arg%" == "NativeAOT"             (set __TestBuildMode=nativeaot&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
 if /i "%arg%" == "Perfmap"               (set __CreatePerfmap=1&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
-if /i "%arg%" == "AllTargets"            (set "__BuildNeedTargetArg=/p:CLRTestBuildAllTargets=%1"&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
+if /i "%arg%" == "AllTargets"            (set "__BuildNeedTargetArg=/p:CLRTestBuildAllTargets=allTargets"&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
 if /i "%arg%" == "ExcludeMonoFailures"   (set __Mono=1&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
 if /i "%arg%" == "Mono"                  (set __Mono=1&set processedArgs=!processedArgs! %1&shift&goto Arg_Loop)
 
@@ -234,7 +234,7 @@ if %__Ninja% == 0 (
     set __CommonMSBuildArgs=%__CommonMSBuildArgs% /p:UseVisualStudioNativeBinariesLayout=true
 )
 
-set __msbuildArgs=%__CommonMSBuildArgs% /nologo /verbosity:minimal /clp:Summary /maxcpucount %__UnprocessedBuildArgs%
+set __msbuildArgs=%__CommonMSBuildArgs% /nologo /verbosity:minimal /clp:Summary /maxcpucount %__BuildNeedTargetArg% %__UnprocessedBuildArgs%
 
 echo %__MsgPrefix%Common MSBuild args: %__msbuildArgs%