Backtrace requirement creates inability to build on any musl based system

[ozwaldorf]

Due to musl not having backtrace support, systems such as Void (musl) and Alpine that use musl instead of glibc cannot build.

[se@xps ~]$ go get github.com/keroserene/go-webrtc
# github.com/keroserene/go-webrtc
go/src/github.com/keroserene/go-webrtc/lib/libwebrtc-linux-amd64-magic.a(checks.o): In function `rtc::DumpBacktrace()':
../../webrtc/base/checks.cc:(.text._ZN3rtc13DumpBacktraceEv+0x30): undefined reference to `backtrace'
../../webrtc/base/checks.cc:(.text._ZN3rtc13DumpBacktraceEv+0x3c): undefined reference to `backtrace_symbols'
collect2: error: ld returned 1 exit status

[arlolra]

Looks like this is guarded by __GLIBCXX__

https://webrtc.googlesource.com/src/+/c279861207c5b15fc51069e96595782350e0ac12/webrtc/base/checks.cc#63

but you'll need to compile the magic library yourself. Please see the build.sh script.