Reverting some changes for older gcc compiler (<5.0).
Reverting some changes for older gcc compiler (<5.0).

shikhar413/openmc,smharper/openmc,paulromano/openmc,wbinventor/openmc,mit-crpg/openmc,johnnyliu27/openmc,liangjg/openmc,smharper/openmc,wbinventor/openmc,mit-crpg/openmc,paulromano/openmc,walshjon/openmc,johnnyliu27/openmc,walshjon/openmc,walshjon/openmc,walshjon/openmc,paulromano/openmc,amandalund/openmc,liangjg/openmc,shikhar413/openmc,wbinventor/openmc,liangjg/openmc,shikhar413/openmc,amandalund/openmc,amandalund/openmc,paulromano/openmc,amandalund/openmc,johnnyliu27/openmc,smharper/openmc,shikhar413/openmc,mit-crpg/openmc,mit-crpg/openmc,liangjg/openmc,smharper/openmc,wbinventor/openmc,johnnyliu27/openmc