cmake HAVE_PRE_BAR_RESTRICT examples

mmp/pbrt-v4 CMakeLists.txt :478 

check_cxx_source_compiles (
"int * __restrict ptr;
int main() { }"
HAVE_PRE_BAR_RESTRICT)

mmp/pbrt-v4 CMakeLists.txt :485 

elseif (HAVE_PRE_BAR_RESTRICT)