v3: Jemalloc and LLVM Flang Support

This release of ESMA_cmake v3 adds a new FindJeMalloc.cmake file for optional use in GEOS as well as preliminary LLVMFlang support.

Note that use of JeMalloc requires having the JeMalloc library available as well as changes in CMake for the needed executable.

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From CHANGELOG.md

• Add FindJeMalloc.cmake for use with builds of GEOSgcm
• Add preliminary LLVMFlang support

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What's Changed

• Add FindJeMalloc.cmake (v3 branch) by @mathomp4 in #396
• v3: Add preliminary Flang support by @mathomp4 in #401

Full Changelog: v3.50.0...v3.51.0