Use same std version as LLVM, see rhbz#1817631

pocl.spec

@@ -5,7 +5,7 @@ Summary:        Portable Computing Language - an OpenCL implementation
 Name:           pocl
 %global ver 1.5
 Version:        %{lua:ver = string.gsub(rpm.expand("%{ver}"), "-", "~"); print(string.lower(ver))}
-Release:        2%{?dist}
+Release:        3%{?dist}
 
 # The whole code is under MIT
 # except include/utlist.h which is under BSD (and unbundled) and
@@ -89,7 +89,6 @@ pushd %{_target_platform}
 %ifarch aarch64 %{arm}
     -DLLC_HOST_CPU="generic" \
 %endif
-    -DENABLE_LATEST_CXX_STD=ON \
     -DPOCL_ICD_ABSOLUTE_PATH=OFF \
     %{nil}
     # -DENABLE_TESTSUITES=all Requires clBLAS
@@ -133,6 +132,9 @@ popd
 %{_libdir}/pkgconfig/%{name}.pc
 
 %changelog
+* Thu Apr 23 2020 sguelton@redhat.com - 1.5-3
+- Use same std version as LLVM, see rhbz#1817631
+
 * Sun Apr 05 2020 sguelton@redhat.com - 1.5-2
 - rebuilt for llvm 10.0.0 final