Backtrace is not available on non-glibc systems

I'm trying to build Sink for Alpine Linux and postmarketOS which use Musl rather than glibc, but compilation fails because of the use of the GNUism backtrace.

/usr/lib/gcc/x86_64-alpine-linux-musl/9.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: CMakeFiles/sink_synchronizer.dir/backtrace.cpp.o: in function `printStacktrace()':
backtrace.cpp:(.text+0x179): undefined reference to `backtrace'
/usr/lib/gcc/x86_64-alpine-linux-musl/9.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: backtrace.cpp:(.text+0x187): undefined reference to `backtrace_symbols'