Improve handling of gmock and gcc6
This patch reverts commit
d6e35c96 that used gcc
-fno-delete-null-pointer-checks to work around implementation errors
in gmock 1.7. There's been no new release of gmock for several years,
but a patch is now available to address this issue.
This commit applies that patch, found at
https://github.com/google/googletest/issues/705#issuecomment-
235067917. Updated
our README describing modifications GROMACS has found it necessary to
make.
Fixes #1911
Change-Id: I0d5abe9bf8172f6749bcad97a13765edaa3d4c80