Make MTProxy compatible with non-glibc systems

[marshall-lee]

MTProxy relies on some specific glibc features that not every libc supports. So if one wants to compile it on Alpine Linux some tweaks are required. I successfully compiled MTProxy with musl libc by doing the following:

• backtrace function is non-standard. Use libexecinfo port if it's available in the system.
• Change lrand48_r, mrand48_r, drand48_r, rand48_r to their standard counterparts.
• Add -fcommon option to fix the build on the latest GCC versions.