exclude obj/cmake from codeql.

[mangod9]

There are duplicate issues being created due to random directory names generated by cmake in obj/cmake

[GrabYourPitchforks]

These are not duplicate issues in the sense that there's no "primary" issue (outside the CMakeFiles folder) that they're duplicates of.

Instead, what should probably be done here is to suppress the specific files that we know are generating false positives. The pattern would presumably look something like:

artifacts/obj/**/CMakeFiles/**/CheckFunctionExists.c

[GrabYourPitchforks]

The comment justifying this suppression is inaccurate. The comment doesn't describe why this file specifically is targeted.

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