Disable __thread for clang when building shared libraries on Mac OSX.
Disable __thread for clang when building shared libraries on Mac OSX.

I was not able to create a configure test that actually failed to link
on OSX with Clang building shared libraries, so instead I have explicitly
disabled __thread for this particular case, since we know for a fact that
it doesn't link currently.

hrittich/libmesh,dschwen/libmesh,vikramvgarg/libmesh,friedmud/libmesh,pbauman/libmesh,salazardetroya/libmesh,jiangwen84/libmesh,roystgnr/libmesh,vikramvgarg/libmesh,dmcdougall/libmesh,dknez/libmesh,Mbewu/libmesh,balborian/libmesh,balborian/libmesh,vikramvgarg/libmesh,balborian/libmesh,pbauman/libmesh,coreymbryant/libmesh,pbauman/libmesh,BalticPinguin/libmesh,libMesh/libmesh,Mbewu/libmesh,Mbewu/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,jwpeterson/libmesh,90jrong/libmesh,permcody/libmesh,salazardetroya/libmesh,coreymbryant/libmesh,dknez/libmesh,salazardetroya/libmesh,libMesh/libmesh,giorgiobornia/libmesh,roystgnr/libmesh,aeslaughter/libmesh,giorgiobornia/libmesh,dschwen/libmesh,capitalaslash/libmesh,permcody/libmesh,balborian/libmesh,salazardetroya/libmesh,dmcdougall/libmesh,markcmiller86/libmesh_silo,friedmud/libmesh,90jrong/libmesh,vikramvgarg/libmesh,dmcdougall/libmesh,friedmud/libmesh,svallaghe/libmesh,balborian/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,karpeev/libmesh,karpeev/libmesh,libMesh/libmesh,libMesh/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,aeslaughter/libmesh,dknez/libmesh,roystgnr/libmesh,markcmiller86/libmesh_silo,jiangwen84/libmesh,benkirk/libmesh,salazardetroya/libmesh,dschwen/libmesh,permcody/libmesh,markcmiller86/libmesh_silo,dschwen/libmesh,dmcdougall/libmesh,dknez/libmesh,karpeev/libmesh,giorgiobornia/libmesh,svallaghe/libmesh,giorgiobornia/libmesh,libMesh/libmesh,aeslaughter/libmesh,balborian/libmesh,90jrong/libmesh,hrittich/libmesh,Mbewu/libmesh,90jrong/libmesh,hrittich/libmesh,Mbewu/libmesh,dknez/libmesh,svallaghe/libmesh,karpeev/libmesh,vikramvgarg/libmesh,libMesh/libmesh,markcmiller86/libmesh_silo,hrittich/libmesh,balborian/libmesh,aeslaughter/libmesh,balborian/libmesh,jiangwen84/libmesh,jwpeterson/libmesh,pbauman/libmesh,90jrong/libmesh,coreymbryant/libmesh,markcmiller86/libmesh_silo,jiangwen84/libmesh,permcody/libmesh,dmcdougall/libmesh,salazardetroya/libmesh,markcmiller86/libmesh_silo,capitalaslash/libmesh,salazardetroya/libmesh,roystgnr/libmesh,vikramvgarg/libmesh,permcody/libmesh,vikramvgarg/libmesh,aeslaughter/libmesh,dschwen/libmesh,aeslaughter/libmesh,markcmiller86/libmesh_silo,friedmud/libmesh,jiangwen84/libmesh,90jrong/libmesh,jiangwen84/libmesh,libMesh/libmesh,benkirk/libmesh,coreymbryant/libmesh,pbauman/libmesh,capitalaslash/libmesh,friedmud/libmesh,BalticPinguin/libmesh,dmcdougall/libmesh,aeslaughter/libmesh,dknez/libmesh,pbauman/libmesh,pbauman/libmesh,dschwen/libmesh,vikramvgarg/libmesh,giorgiobornia/libmesh,BalticPinguin/libmesh,cahaynes/libmesh,giorgiobornia/libmesh,benkirk/libmesh,benkirk/libmesh,dmcdougall/libmesh,friedmud/libmesh,jiangwen84/libmesh,pbauman/libmesh,BalticPinguin/libmesh,90jrong/libmesh,balborian/libmesh,hrittich/libmesh,dmcdougall/libmesh,dschwen/libmesh,roystgnr/libmesh,hrittich/libmesh,friedmud/libmesh,aeslaughter/libmesh,permcody/libmesh,cahaynes/libmesh,salazardetroya/libmesh,90jrong/libmesh,karpeev/libmesh,cahaynes/libmesh,benkirk/libmesh,markcmiller86/libmesh_silo,Mbewu/libmesh,roystgnr/libmesh,svallaghe/libmesh,dknez/libmesh,svallaghe/libmesh,jwpeterson/libmesh,Mbewu/libmesh,cahaynes/libmesh,coreymbryant/libmesh,benkirk/libmesh,cahaynes/libmesh,hrittich/libmesh,karpeev/libmesh,jiangwen84/libmesh,svallaghe/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,benkirk/libmesh,pbauman/libmesh,karpeev/libmesh,capitalaslash/libmesh,hrittich/libmesh,permcody/libmesh,friedmud/libmesh,vikramvgarg/libmesh,aeslaughter/libmesh,libMesh/libmesh,capitalaslash/libmesh,dschwen/libmesh,svallaghe/libmesh,balborian/libmesh,Mbewu/libmesh,jwpeterson/libmesh,friedmud/libmesh,cahaynes/libmesh,giorgiobornia/libmesh,90jrong/libmesh,coreymbryant/libmesh,karpeev/libmesh,jwpeterson/libmesh,svallaghe/libmesh,coreymbryant/libmesh,benkirk/libmesh,capitalaslash/libmesh,roystgnr/libmesh,coreymbryant/libmesh,Mbewu/libmesh,svallaghe/libmesh,benkirk/libmesh,giorgiobornia/libmesh,cahaynes/libmesh,jwpeterson/libmesh,dknez/libmesh,hrittich/libmesh,permcody/libmesh,giorgiobornia/libmesh,cahaynes/libmesh