fix several gtags related issues: mission update_gtags.cmd & lack of execution permission

autoload/gutentags.vim

@@ -103,7 +103,11 @@ endfunction
 " into a list of unquoted arguments on Unix/Mac.
 if has('win32') || has('win64')
     function! gutentags#make_args(cmd) abort
-        return join(a:cmd, ' ')
+        if &shell == 'pwsh' || &shell == 'powershell'
+            return '& ' . join(a:cmd, ' ')
+        else
+            return join(a:cmd, ' ')
+        endif
     endfunction
 else
     function! gutentags#make_args(cmd) abort

plat/win32/update_gtags.cmd

@@ -0,0 +1,56 @@
+@echo off
+
+setlocal EnableExtensions EnableDelayedExpansion
+
+rem ==========================================
+rem PARSE ARGUMENTS
+rem ==========================================
+set "GTAGS_EXE=gtags"
+set "GTAGS_ARGS="
+set "FILE_LIST_CMD="
+
+if [%1]==[] goto :Usage
+
+:ParseArgs
+if [%1]==[] goto :DoneParseArgs
+if [%1]==[-e] (
+	set GTAGS_EXE=%~2
+	shift /1
+	shift /1
+	goto :ParseArgs
+)
+if [%1]==[-L] (
+	set FILE_LIST_CMD=%~2
+	shift /1
+	shift /1
+	goto :ParseArgs
+)
+set "GTAGS_ARGS=%GTAGS_ARGS% %1"
+shift /1
+goto :ParseArgs
+
+:DoneParseArgs
+rem ==========================================
+rem GENERATE GTAGS
+rem ==========================================
+set "GTAGS_CMD=%GTAGS_EXE% %GTAGS_ARGS%"
+if /i not "%FILE_LIST_CMD%"=="" (
+	set "GTAGS_CMD=%FILE_LIST_CMD% | %GTAGS_EXE% -f- %GTAGS_ARGS%"
+)
+echo Running gtags:
+echo "%GTAGS_CMD%"
+call %GTAGS_CMD%
+echo Done.
+goto :EOF
+rem ==========================================
+rem USAGE
+rem ==========================================
+
+:Usage
+echo Usage:
+echo %~n0 ^<options^>
+echo.
+echo -e [exe=gtags]: The gtags executable to run.
+echo -L [cmd=]: The file list command to run
+echo.
+