A better way to fix this and avoid this from happening again is to enable the --with-x=yes in the easyblock used to build R, on the condition that X11 is listed as a dependency, and use --with-x=no otherwise, unless --with-x is already specified in the configopts obtained from the easyconfig file.

The same applies to many other configure options, so doing this properly isn't something I have time for right now...

Test report by @boegel
SUCCESS
Build succeeded for 3 out of 3 (3 easyconfigs in this PR)
node2422.golett.os - Linux centos linux 7.3.1611, Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz, Python 2.7.5
See https://gist.github.com/d0f558548e4ed52a7da31a2c8303843a for a full test report.

Test report by @boegel
SUCCESS
Build succeeded for 3 out of 3 (3 easyconfigs in this PR)
node2110.delcatty.os - Linux centos linux 7.3.1611, Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz, Python 2.7.5
See https://gist.github.com/32f8ca52227d0131f3b51fb1fbfd2764 for a full test report.