CMake: Fix openmp-simd configuration
CMake: Fix openmp-simd configuration

This enables openmp simd for Clang version 3.6 or newer (and the
corresponding version for XCode). Further, it unconditionally disables
the openmp check for any older clang version - checking for openmp support
with the flag only is unreliable

naliboff/dealii,gpitton/dealii,gpitton/dealii,naliboff/dealii,andreamola/dealii,Arezou-gh/dealii,YongYang86/dealii,JaeryunYim/dealii,nicolacavallini/dealii,jperryhouts/dealii,danshapero/dealii,JaeryunYim/dealii,maieneuro/dealii,Arezou-gh/dealii,EGP-CIG-REU/dealii,kalj/dealii,sairajat/dealii,gpitton/dealii,Arezou-gh/dealii,shakirbsm/dealii,nicolacavallini/dealii,EGP-CIG-REU/dealii,EGP-CIG-REU/dealii,angelrca/dealii,YongYang86/dealii,YongYang86/dealii,gpitton/dealii,kalj/dealii,johntfoster/dealii,andreamola/dealii,EGP-CIG-REU/dealii,maieneuro/dealii,Arezou-gh/dealii,angelrca/dealii,YongYang86/dealii,maieneuro/dealii,gpitton/dealii,YongYang86/dealii,pesser/dealii,shakirbsm/dealii,sairajat/dealii,naliboff/dealii,kalj/dealii,nicolacavallini/dealii,johntfoster/dealii,Arezou-gh/dealii,sairajat/dealii,adamkosik/dealii,andreamola/dealii,andreamola/dealii,ESeNonFossiIo/dealii,andreamola/dealii,sairajat/dealii,johntfoster/dealii,YongYang86/dealii,maieneuro/dealii,ESeNonFossiIo/dealii,andreamola/dealii,jperryhouts/dealii,ESeNonFossiIo/dealii,ibkim11/dealii,danshapero/dealii,EGP-CIG-REU/dealii,ESeNonFossiIo/dealii,jperryhouts/dealii,pesser/dealii,sairajat/dealii,spco/dealii,kalj/dealii,Arezou-gh/dealii,danshapero/dealii,naliboff/dealii,pesser/dealii,adamkosik/dealii,jperryhouts/dealii,spco/dealii,maieneuro/dealii,ibkim11/dealii,ibkim11/dealii,angelrca/dealii,ibkim11/dealii,angelrca/dealii,JaeryunYim/dealii,kalj/dealii,naliboff/dealii,shakirbsm/dealii,maieneuro/dealii,shakirbsm/dealii,ESeNonFossiIo/dealii,kalj/dealii,johntfoster/dealii,nicolacavallini/dealii,pesser/dealii,ESeNonFossiIo/dealii,nicolacavallini/dealii,angelrca/dealii,nicolacavallini/dealii,sairajat/dealii,jperryhouts/dealii,maieneuro/dealii,danshapero/dealii,naliboff/dealii,angelrca/dealii,shakirbsm/dealii,shakirbsm/dealii,gpitton/dealii,johntfoster/dealii,adamkosik/dealii,naliboff/dealii,spco/dealii,johntfoster/dealii,adamkosik/dealii,nicolacavallini/dealii,pesser/dealii,adamkosik/dealii,spco/dealii,shakirbsm/dealii,JaeryunYim/dealii,JaeryunYim/dealii,JaeryunYim/dealii,sairajat/dealii,ibkim11/dealii,EGP-CIG-REU/dealii,YongYang86/dealii,adamkosik/dealii,andreamola/dealii,danshapero/dealii,adamkosik/dealii,pesser/dealii,danshapero/dealii,johntfoster/dealii,Arezou-gh/dealii,spco/dealii,pesser/dealii,EGP-CIG-REU/dealii,jperryhouts/dealii,angelrca/dealii,jperryhouts/dealii,ibkim11/dealii,spco/dealii,JaeryunYim/dealii,ESeNonFossiIo/dealii,gpitton/dealii,kalj/dealii,danshapero/dealii,ibkim11/dealii,spco/dealii