This is a follow-up commit for commit 82c2461e, where the default build is
to use the PCRE that is installed in the system, if it is available and is
not overridden with --with-internal-pcre.

For Visual Studio builds, this means that the new 'Debug' and 'Release'
configs will now use PCRE that is found on the system, which were renamed
from the '*_ExtPCRE' configs; and that there are now 'Debug_BundledPCRE'
and 'Release_BundledPCRE' configs which make use of the PCRE that is
supplied with the GLib sources, which, replaces the former 'Debug' and
'Release' configs.