benchmark graphics-magick not using openmp with clang

[Mike.bench]

When running "phoronix-test-suite benchmark graphics-magick" on Ubuntu I see almost 10X better performance with gcc (12.2.0 - default compiler) vs clang (15.0.7 - set via export CC=clang and CXX=clang++).

A key difference (which I suspect is cause of large perf difference) that gcc is using openmp while clang is not. When I look at the install.log for both runs I see the option "-fopenmp" in the gcc run but this option (and some others) are missing in the clang run.

So, root question is how do I get graphics-magick benchmark to use openmp options when using clang.

[Mike.bench]

Some more info in case this helps. Trying to figure out why -fopenmp not passed to clang and the difference seems to occur pretty early - in the pts-install.json file.

I have no idea how this file is created (and why different). Are there and suggestions / docs on how to debug why different?

E.g.

CC/CXX not set:
"compiler_data": {
"compiler-type": "CC",
"compiler": "gcc",
"compiler-options": "-fopenmp -O2 -ljpeg -lSM -lICE -lX11 -lxml2 -lz -lm -lpthread"
},

CC/CXX set to clang/clang++
"compiler_data": {
"compiler-type": "CC",
"compiler": "clang",
"compiler-options": "-O2 -ljpeg -lSM -lICE -lX11 -lxml2 -lz -lm -lpthread"
},