Building recomp.cpp fails on alpine (undefined reference to `backtrace')

[mkst]

Compile log:

#0 8.193 /ido-static-recomp/recomp.cpp:3711: undefined reference to `backtrace'
#0 8.193 /usr/lib/gcc/i586-alpine-linux-musl/11.2.1/../../../../i586-alpine-linux-musl/bin/ld: /ido-static-recomp/recomp.cpp:3712: undefined reference to `backtrace_symbols'
#0 8.225 collect2: error: ld returned 1 exit status
#0 8.227 make[1]: *** [Makefile:169: build/recomp.elf] Error 1
#0 8.227 make[1]: Leaving directory '/ido-static-recomp'
#0 8.227 make: *** [Makefile:148: setup] Error 2

This can be fixed by linking against libexecinfo (i.e. ensuring libexecinfo-dev is installed and adding -lexecinfo to LDFLAGS).

I'm happy to submit a PR, but it feels a little awkward to determine the flavour of Linux in the Makefile - open to suggestions!

[AngheloAlf]

We should probably make the traceback stuff toggleable with an ifdef, and turn it off by default, since it isn't a feature that we use much
For now you could comment out the #define UNIX_PLATFORM line and it should build fine in your distro