wfmash now builds with clang

[pjotrp]

Includes a code fix that would not compile on clang with openmp d32f814.

Also guix and cmake fixes and added some tests that are now in github actions(?!):

[100%] Linking CXX executable bin/wfmash
[100%] Built target wfmash
wrk@napoli /export/local/home/wrk/iwrk/opensource/code/pangenome/wfmash/build [env]$ ctest .
Test project /export/local/home/wrk/iwrk/opensource/code/pangenome/wfmash/build
    Start 1: wfmash-time-LPA
1/5 Test #1: wfmash-time-LPA .......................................   Passed   10.27 sec
    Start 2: wfmash-subset-LPA-to-SAM
2/5 Test #2: wfmash-subset-LPA-to-SAM ..............................   Passed   11.89 sec
    Start 3: wfmash-mapping-coverage-with-8-yeast-genomes-to-PAF
3/5 Test #3: wfmash-mapping-coverage-with-8-yeast-genomes-to-PAF ...   Passed   30.20 sec
    Start 4: wfmash-short-reads-500bps-to-SAM
4/5 Test #4: wfmash-short-reads-500bps-to-SAM ......................   Passed   65.74 sec
    Start 5: wfmash-short-reads-255bps-to-PAF
5/5 Test #5: wfmash-short-reads-255bps-to-PAF ......................   Passed    0.91 sec

100% tests passed, 0 tests failed out of 5