CxxUtils: fix checkergcc plugin configuration
The ATLAS_USE_GCC_CHECKERS
option is not set yet when
CxxUtilsSettingsConfig
is being executed. Remove the check as the same
check is anyway done as part of AtlasCompilerSettings
in
atlasexternals.
Relates to ATLINFR-4570.
full-build to make sure all source files are being recompiled/rechecked.