Bug 1776255 - Add the appropriate 'when' to all 'option' that end up calling...

Bug 1776255 - Add the appropriate 'when' to all 'option' that end up calling 'pkg_check_modules' later r=firefox-build-system-reviewers,glandium

We don't check for pkg-config on some platforms (Windows, OSX, Android).
On those platforms, calling 'pkg_check_modules' will not work. Adding
the same 'when' used for the 'pkg_config' check to all the options that
end up calling 'pkg_check_modules' effectively disables them, and prevents
'pkg_check_modules' from being called.

Differential Revision: https://phabricator.services.mozilla.com/D150649