Following statement copied from https://www.crystax.net/android/ndk (15.12.2019):
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License
The content of the CrystaX NDK is covered by various open-source licenses. See the copyright disclaimers in each respective file for details.

Note that the CrystaX NDK release packages also contain prebuilt binaries for the compiler, linker, archiver, etc. The source codes for the toolchains are available at GitHub (you can use the build script to download it automatically).

The prebuilt GCC and companion binaries (GDB, binutils etc) are covered by either the GNU General Public License (GPL) or the GNU Lesser General Public License (LGPL). For details, see the files COPYING and COPYING.LIB under $NDK/toolchains/$tc/prebuilt/$system.

The prebuilt LLVM/Clang toolchains are covered by the LLVM "BSD" license.

Basically, licensing rules are the same as for Google's Android NDK - i.e., both commercial and non-commercial usage allowed. The only additions are regarding CrystaX parts, which are covered by a permissive BSD 2-clause license.