CMake: Fix a test for bug in LLVM that incorrectly stated it's checking for assertions; it's checking for LLVM's debugging support.
CMake: Fix a test for bug in LLVM that incorrectly stated it's checking
for assertions; it's checking for LLVM's debugging support.

franz/pocl,Oblomov/pocl,0charleschen0/pocl,pocl/pocl,jrprice/pocl,vkorhonen/pocl,vkorhonen/pocl,Oblomov/pocl,vkorhonen/pocl,pocl/pocl,0charleschen0/pocl,rjodin/pocl,pavanky/pocl,franz/pocl,pavanky/pocl,Oblomov/pocl,dsandersimgtec/pocl,rjodin/pocl,pocl/pocl,pavanky/pocl,pavanky/pocl,jrprice/pocl,dsandersimgtec/pocl,jrprice/pocl,dsandersimgtec/pocl,Oblomov/pocl,0charleschen0/pocl,pocl/pocl,0charleschen0/pocl,Oblomov/pocl,rjodin/pocl,pocl/pocl,franz/pocl,rjodin/pocl,jrprice/pocl,franz/pocl,dsandersimgtec/pocl,vkorhonen/pocl,franz/pocl