Ninja Multi-Config: Fix issue with "all" in CMAKE_NMC_DEFAULT_CONFIGS
Prior to this fix, CMAKE_NMC_DEFAULT_CONFIGS would inherit "all" from the union of CMAKE_NMC_DEFAULT_BUILD_FILE_CONFIG and CMAKE_NMC_CROSS_CONFIGS. This is inconsistent with the behavior of the "all" target signifying CMAKE_NMC_CROSS_CONFIGS. Update "all" in CMAKE_NMC_DEFAULT_CONFIGS to inherit only from CMAKE_NMC_CROSS_CONFIGS.
Backport: release
Edited by Kyle Edwards