Clean up compiler flag specification

[fmahebert]

Description

As a first step towards cleaning JEDI's specification of compilers flags, this PR reorganizes and changes flags as follows:

• a new file cmake/build_type_compiler_flags.cmake provides default build-type compiler flags for compilers not in ecbuild; this could eventually be contributed upstream. This file should be identical in all JEDI repos.
• a new file cmake/jedi_common_compiler_flags.cmake provides JEDI specific compiler flags; for example warning levels, floating-point behavior, etc. This file should be identical in all JEDI repos.
• repo-specific compiler flags

This has been tested with gcc13, IntelLLVM 2025.3, Intel mixing icx with legacy ifort; and also with Cray by David Davies at UKMO. In general, for these compilers, the cleaned up flags have fewer runtime floating-point issues, and more compile-time warnings.

Issue(s) addressed

This is work towards https://github.com/JCSDA-internal/CI/issues/173

Dependencies

Part of a large family of PRs, see the CI issue for a complete list. These do not strictly depend on each other.

Impact

Impact on users:

• expect change in warnings emitted
• when using Intel LLVM, possible small changes to floating-point values as a result of changing floating-point handling
• this has not been tested with all compilers, so users of less-common compilers may need to iterate on the flags

Checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have run the unit tests before creating the PR

[shlyaeva]

Thank you for fixing soca @fmahebert! I did not review CMakeLists changes (not an expert), but the code changes and reference changes look good to me.

[ytremolet]

Thank you for fixing soca @fmahebert! I did not review CMakeLists changes (not an expert), but the code changes and reference changes look good to me.

@shlyaeva Can you approve the PR?