Use vswhere to set environment variables for MSVS 2017

Allow building official releases with MSVS 2017 without doing it from
its "developer command prompt" by using the vswhere utility to set up
the paths correctly.

Closes #18083.

build/tools/msvs/findvs.bat

@@ -0,0 +1,54 @@
+@echo off
+
+rem This is used to set up the VS2017 and later (hopefully) environment.
+
+rem Called with two paramaters, the inclusive low and the exclusisve high.
+if "%1" == "" goto ERR_NOPARM
+if "%2" == "" goto ERR_NOPARM
+
+rem If not running from official build, remember where we are.
+
+if "%curr_dir%" == "" (
+  set curr_dir=%cd%
+)
+
+@echo Checking if vswhere in path
+vswhere 1>nul
+
+if errorlevel 9009 (
+@echo "vswhere not found, trying C:\Program Files (x86)\Microsoft Visual Studio\Installer"
+set "PATH=C:\Program Files (x86)\Microsoft Visual Studio\Installer;%PATH%"
+)
+
+vswhere 1>nul
+if errorlevel 9009 (
+@echo "vswhere not found"
+goto ERR_EXIT
+)
+
+for /f "usebackq tokens=*" %%i in (`vswhere -latest -version "[%1,%2)" -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do (
+  set InstallDir=%%i
+)
+
+if "%InstallDir%" == "" (
+  @echo Install directory not found
+  goto ERR_EXIT
+)
+
+if NOT exist "%InstallDir%\Common7\Tools\vsdevcmd.bat" (
+  @echo Can't find an vsdevcmd.bat
+  goto ERR_EXIT
+)
+
+call "%InstallDir%"\Common7\Tools\vsdevcmd.bat
+
+rem Go back to where we were before vsdevcmd changed things.
+cd %curr_dir%
+
+goto end
+
+:ERR_NOPARM
+@echo Need to specifiy version min/max range, eg.: 15.0 16.0
+:ERR_EXIT
+exit /b 1
+:end

build/tools/msvs/officialbuild.bat

@@ -1,4 +1,6 @@
-ECHO ON
+@echo off
+
+rem SetLocal EnableDelayedExpansion
 
 if "%1" == "" goto ERR_NOPARM
 
@@ -22,12 +24,21 @@ set compvers="Unknown"
 
 if "%1" == "vc141" (
   @echo Building for vc141 / vs2017
-  @echo This will only work if the environment varialbe VS150COMNTOOLS is set
-  @echo or a VS2017 command prompt is used.
   set comp=141
   set compvers=vc141
+
+  if NOT "%VS150COMNTOOLS%" == "" (
     call "%VS150COMNTOOLS%VsDevCmd.bat"
   )
+  if "%VS150COMNTOOLS%" == "" (
+    call %curr_dir%\findvs 15.0 16.0
+
+    if errorlevel 1 (
+      @echo vswhere.exe must be in your path or a VS2017 developer command prompt must be used.
+      goto end
+    )
+  )
+)
 if "%1" == "vc140" (
   @echo Building for vc140 / vs2015
   set comp=140