Tests: Fix RunCMake infrastructure for LCC and CMP0129

Brad Kingrequested to merge
brad.king/cmake:test-lcc-cmp0129 into master

Since !6643 (merged) we intended to enable policy CMP0129 in RunCMake tests via -DCMAKE_POLICY_DEFAULT_CMP0129=NEW. Fix the condition activating that to check CMAKE_C_COMPILER_ID where it is always available.

Remove now-unnecessary CMP0129 settings in RunCMake cases.

Edited by Brad King

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