Append SLES version at NCCS

This release append -SLES12 or -SLES15 on the build and install directories at NCCS when using build.csh (→ parallel_build.csh) to make it clear to users where they built.

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From CHANGELOG.md

Fixed

• Append -SLES12 or -SLES15 on the build and install directories at NCCS when using build.csh to make it clear to users

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What's Changed

• Append SLES version to build by @mathomp4 in #103

Full Changelog: v4.20.1...v4.20.2