Massimiliano Culpo c52426ea7a Make clingo the default solver (#25502) ... Modifications: - [x] Change `defaults/config.yaml` - [x] Add a fix for bootstrapping patchelf from sources if `compilers.yaml` is empty - [x] Make `SPACK_TEST_SOLVER=clingo` the default for unit-tests - [x] Fix package failures in the e4s pipeline Caveats: 1. CentOS 6 still uses the original concretizer as it can't connect to the buildcache due to issues with `ssl` (bootstrapping from sources requires a C++14 capable compiler) 1. I had to update the image tag for GitlabCI in e699f14. 1. libtool v2.4.2 has been deprecated and other packages received some update		2021-09-14 22:44:16 -07:00
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spack	Make clingo the default solver (#25502)	2021-09-14 22:44:16 -07:00