Yes, it is. To expand on the situation:
It is designed to act as a drop-in replacement for the GNU Compiler Collection (GCC), supporting most of its compilation flags and unofficial language extensions. Its contributors include Apple, Microsoft, Google, ARM, Sony, Intel and Advanced Micro Devices (AMD). It is open-source software, with source code released under the University of Illinois/NCSA License, a permissive free software licence.
About the licence:
Source code under the NCSA license can be incorporated into proprietary products without the reciprocity requirements that copyleft free software licenses raise. The license is compatible with all versions of the GNU General Public License.
If you care to read more about licences n stuff this page is a good place to start.