Contrib goolf 1.4.20

this goolf uses the same GCC compiler like #928 (GCC/4.7.4) and provides incremental upgrades for all the underlying components; this toolchain is expected to have maximal compatibility with debuggers.

The intention is to use it with recursive --try, to provide debugg-able builds.
I just noticed you bumped this from v1.6.4 in goolf/1.4.10 to v1.7.5 here in goolf/1.4.20

Here's the versioning scheme we have now:

goolf 1.4.x: GCC 4.7.x, OpenMPI 1.6.x
goolf 1.5.x: GCC 4.8.x, OpenMPI 1.6.x
goolf 1.6.x: GCC 4.8.x, OpenMPI 1.7.x
(planned, no PR yet): goolf 1.7.x, OpenMPI 1.8.x

so, this PR jumps out in the sense that it bumps the version of OpenMPI to from 1.6.x to 1.7.x without changing the minor version of the toolchain (note: there's no room for such a bump either in the scheme described above...)