Update Sandcastle Windows test build script (facebook#1268)

Summary:
Pull Request resolved: facebook#1268

Cmake `--parallel` flag on Windows actually reduces parallelism, so
upgrade to VS2019 and use MTT. Also update CircleCI to use the same
flag.

Build time changes (on a Sandcastle Windows VM):
```
# Run command
Before: ~17min
Removing --parallel: ~6min
With MTT flag: ~3min
```

[Facebook] for details, please check our post:
https://fburl.com/workplace/a6mjnirn.

Reviewed By: neildhar

Differential Revision: D52878323

fbshipit-source-id: 06c71701d6b57be7b44d1a3c1e1cc10af2a89669

.circleci/config.yml

@@ -333,7 +333,7 @@ jobs:
           name: Run Hermes regression tests
           command: |
             cmake -S hermes -B build -G 'Visual Studio 16 2019'
-            cmake --build build --target check-hermes
+            cmake --build build --target check-hermes -- -m /p:UseMultiToolTask=true -m /p:EnforceProcessCountAcrossBuilds=true
 
   windows:
     executor:
@@ -396,9 +396,9 @@ jobs:
             if (-not $?) { throw "Failed to configure Hermes" }
             cmake -S hermes -B build_hdb -G 'Visual Studio 16 2019' -Ax64 $Env:RELEASE_FLAGS
             if (-not $?) { throw "Failed to configure Hermes" }
-            cmake --build ./build --config Release
+            cmake --build ./build --config Release -- -m /p:UseMultiToolTask=true -m /p:EnforceProcessCountAcrossBuilds=true
             if (-not $?) { throw "Failed to build Hermes" }
-            cmake --build ./build_hdb --config Release --target hdb
+            cmake --build ./build_hdb --config Release --target hdb -- -m /p:UseMultiToolTask=true -m /p:EnforceProcessCountAcrossBuilds=true
             if (-not $?) { throw "Failed to build Hermes" }
 
       - run: