Fix Cray compiler compatibility for warning flags

[JanStreffing]

The Cray compiler wrapper (CC) does not recognize GCC/Clang-style warning flags like -Wall, -Wextra, etc. This causes CMake configuration to fail with errors like:

CRITICAL - CXX compiler does not recognise CXX flag '-Wall'

This commit wraps all GCC/Clang-style warning flags in a conditional check to skip them when using the Cray compiler, while still applying them for GNU and Clang compilers.

Fixes compilation on Cray HPC systems.

Description

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[JanStreffing]

I see you changed this to NO_FAIL already on the develop branch.
I am a user of OpenIFS 48r1 and Metkit version 1.8.10. I will test wether I can safely update the metkit version downloaded by ecbundle to a version that contains the fix. If so, this can be closed, if not, I will contact Adrian Hill.