CI: Use Visual Studio 2019 for the MSVC CI

...and add ability to select target platform for calling vcvarsall.bat,
so that we can accomodate 32-bit builds and possibly ARM64 builds in the
CI if we need to.

.gitlab-ci.yml

@@ -586,7 +586,7 @@ msys2-clang64:
     paths:
       - _build/meson-logs
 
-vs2017-x64:
+vs2019-x64:
   extends: .only-default
   stage: build
   tags:
@@ -605,6 +605,7 @@ vs2017-x64:
                                --wrap-mode=default
                                --python.platlibdir=C:\Python37\site-packages
                                --python.purelibdir=C:\Python37\site-packages
+                               --plat=x64
   artifacts:
     reports:
       junit:
@@ -621,7 +622,7 @@ vs2017-x64:
       - _build/gthread/libgthread-2.0-0.dll
       - _build/gobject/libgobject-2.0-0.dll
 
-vs2017-x64-static:
+vs2019-x64-static:
   extends: .only-default
   stage: build
   tags:
@@ -641,6 +642,7 @@ vs2017-x64-static:
                                --default-library=static
                                --python.platlibdir=C:\Python37\site-packages
                                --python.purelibdir=C:\Python37\site-packages
+                               --plat=x64
   artifacts:
     reports:
       junit:

.gitlab-ci/test-msvc.bat

@@ -1,15 +1,21 @@
 @echo on
-:: vcvarsall.bat sets various env vars like PATH, INCLUDE, LIB, LIBPATH for the
-:: specified build architecture
-call "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" x64
 
 :: Remove quotes from script args
 setlocal enabledelayedexpansion
 set args=
+set stash_plat=0
+
 for %%x in (%*) do (
-  set args=!args! %%~x
+  if "%%x" == "--plat" set stash_plat=1
+  if "!stash_plat!" == "0" set args=!args! %%~x
+  if "!stash_plat!" == "1" if /i not "%%x" == "--plat" set plat=%%x & set stash_plat=0
 )
 set args=%args:~1%
+if "!plat!" == "" set plat=x64
+
+:: vcvarsall.bat sets various env vars like PATH, INCLUDE, LIB, LIBPATH for the
+:: specified build architecture
+call "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Auxiliary\Build\vcvarsall.bat" !plat!
 
 pip3 install --upgrade --user meson==1.4.2 || goto :error
 meson setup %args% _build || goto :error