Print help for -? and /? cross-plat (#42396)

* Print help for -? and /? cross-plat

build.cmd

@@ -3,6 +3,7 @@ setlocal
 
 set _args=%*
 if "%~1"=="-?" set _args=-help
+if "%~1"=="/?" set _args=-help
 
 powershell -ExecutionPolicy ByPass -NoProfile -Command "& '%~dp0eng\build.ps1'" %_args%
 exit /b %ERRORLEVEL%

eng/build.ps1

@@ -103,7 +103,7 @@ function Get-Help() {
   Write-Host "For more information, check out https://github.com/dotnet/runtime/blob/master/docs/workflow/README.md"
 }
 
-if ($help -or (($null -ne $properties) -and ($properties.Contains('/help') -or $properties.Contains('/?')))) {
+if ($help) {
   Get-Help
   exit 0
 }

eng/build.sh

@@ -172,7 +172,7 @@ while [[ $# > 0 ]]; do
   firstArgumentChecked=1
 
   case "$opt" in
-     -help|-h)
+     -help|-h|-\?|/?)
       usage
       exit 0
       ;;