Fix chpl_regexp.py to support new install path.

The install path changed in e7c4859. This supports the new version.
Fix chpl_gmp.py to support new install path.

The install path changed in e7c4859. This supports the new version.
Merge branch 'master' of github.com:chapel-lang/chapel into chplenv-updates
Merge pull request #95 from thomasvandoren/chplenv-updates

Update chplenv scripts for re2 and gmp to support new install paths.

Commit e7c4859 updated the install paths for several third-party libraries to include the architecture. The `chpl_regexp.py` and `chpl_gmp.py` scripts detect if the associated library has been built, and if so, default to enabling them. This updates those scripts to look at the new install path.