Fixes #4858: Really apply GCC ignore-TKR functionality to v1.8 branch

NOTE: This config/ompi_fortran_check_ignore_tkr.m4 was supposed to be
applied to the v1.7 branch was back for v1.7.5, but somehow r30152
from CMR #4058 wasn't applied properly, and this .m4 patch was not
applied.

This CMR applies the missed the .m4 portion of r30152 to the v1.8
branch.

---svn-pre-commit-ignore-below---

r30152 [[BR]]
Thanks to a reminder from Tobias Burunus, commit support for the
upcoming GCC/gfortran 4.9's ignore TKR interface.

This was originally committed in a side mercurial repo, but I sadly
completely forgot about it until Tobias reminded me.

cmr=v1.7.5:reviewer=dgoodell:subject=Add support for gfortran 4.9 Fortran ignore TKR