Add support for detecting Intel 18.
Add support for detecting Intel 18.

This bug recently hit an Intel 18 user whose compiler was actually
detected to be Intel 8 (a compiler from circa 2004!) due to the
overzealous pattern matching used in compiler.m4.

A larger question is whether we should being removing support for
older compilers, especially those that don't support C++11, since we
now require that in the library.

hrittich/libmesh,jwpeterson/libmesh,giorgiobornia/libmesh,pbauman/libmesh,BalticPinguin/libmesh,hrittich/libmesh,hrittich/libmesh,90jrong/libmesh,90jrong/libmesh,BalticPinguin/libmesh,libMesh/libmesh,dschwen/libmesh,giorgiobornia/libmesh,pbauman/libmesh,roystgnr/libmesh,balborian/libmesh,balborian/libmesh,roystgnr/libmesh,hrittich/libmesh,libMesh/libmesh,hrittich/libmesh,pbauman/libmesh,giorgiobornia/libmesh,capitalaslash/libmesh,90jrong/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,giorgiobornia/libmesh,jwpeterson/libmesh,90jrong/libmesh,jwpeterson/libmesh,hrittich/libmesh,pbauman/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,pbauman/libmesh,BalticPinguin/libmesh,dschwen/libmesh,balborian/libmesh,90jrong/libmesh,libMesh/libmesh,libMesh/libmesh,BalticPinguin/libmesh,libMesh/libmesh,giorgiobornia/libmesh,dschwen/libmesh,hrittich/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,giorgiobornia/libmesh,libMesh/libmesh,90jrong/libmesh,dschwen/libmesh,roystgnr/libmesh,roystgnr/libmesh,90jrong/libmesh,roystgnr/libmesh,hrittich/libmesh,dschwen/libmesh,roystgnr/libmesh,jwpeterson/libmesh,balborian/libmesh,giorgiobornia/libmesh,balborian/libmesh,capitalaslash/libmesh,balborian/libmesh,capitalaslash/libmesh,pbauman/libmesh,dschwen/libmesh,90jrong/libmesh,balborian/libmesh,capitalaslash/libmesh,giorgiobornia/libmesh,capitalaslash/libmesh,90jrong/libmesh,hrittich/libmesh,libMesh/libmesh,pbauman/libmesh,pbauman/libmesh,pbauman/libmesh,jwpeterson/libmesh,dschwen/libmesh,capitalaslash/libmesh,roystgnr/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,balborian/libmesh,giorgiobornia/libmesh,jwpeterson/libmesh,balborian/libmesh,balborian/libmesh