Replace deprecated CMAKE_COMPILER_IS_GNU(CC|CXX) with CMAKE_(C|CXX)_COMPILER_ID

[brad0]

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Description

Replace deprecated use of CMAKE_COMPILER_IS_GNU(CC|CXX) with CMAKE_(C|CXX)COMPILER_ID throughout the tree. Some places already use CMAKE(C|CXX)_COMPILER_ID.

As of CMake 3.24 CMAKE_COMPILER_IS_GNU(CC|CXX) are deprecated and should be replaced with CMAKE_(C|CXX)_COMPILER_ID which were introduced with CMake 2.6.

How can this PR be tested?

Build and check the various paths are taken as appropriate.

Basing the PR against the correct MariaDB version

• [ ] This is a new feature or a refactoring, and the PR is based against the main branch.
• [x] This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• [x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [x] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.