Add support for cosmopolitan compiler

[bnjmnjrk]

Describe the problem you are trying to solve.
Whenever I compile the dist files with the cosmo compiler, I get errors about missing includes like execinfo.h and missing functions like strcat_s.

cosmo link: https://github.com/jart/cosmopolitan

Describe the solution you'd like.
I suspect that adding support for the COSMO compiler is easy, as it adds the __COSMOCC__ preprocessor directive, with which we can easily use the strcat instead of the strcat_s functions (#define ECS_TARGET_POSIX, Cosmo generates POSIX approved polyglots ~see their readme), and disable execinfo (#define HAVE_EXECINFO 0).

The only thing I don't know is how to generate the dist files, is there a shell script somewhere?