Add registry keys to ensure XHR tests can find Perl

(From https://bugs.webkit.org/show_bug.cgi?id=188039.)

90 tests under `http/tests/xmlhttprequest` fail if Perl can't be located.

Solution:
```
reg add HKEY_CLASSES_ROOT\.pl\Shell\ExecCGI\Command /ve /d "C:\tools\perl\perl\bin\perl.exe -T"
reg add HKEY_CLASSES_ROOT\.cgi\Shell\ExecCGI\Command /ve /d "C:\tools\perl\perl\bin\perl.exe -T"
```