Drop quotes from Makefile.am variable.
Drop quotes from Makefile.am variable.

These did not hurt anything, but the quotes get passed to the compiler
itself, which is inconsistent with the way we pass other arguments.

This was originally added in d9684854f by @hrittich, so hopefully it
is not required for Windows.

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