Add GCC_COLORS to preserved envvars

GCC_COLORS is used to colorize the gcc output and changing it can be useful
because some of the defaults may be hard to read on certain terminals.

Author: parejkoj

python/lsst/sconsUtils/state.py

@@ -204,6 +204,7 @@ def _initEnvironment():
         "XPA_PORT",
         "CONDA_BUILD_SYSROOT",
         "SDKROOT",
+        "GCC_COLORS",
     ]
 
     codeCheckerVars = [