Add retcode error checking, solc_binary argument
Add retcode error checking, solc_binary argument

Mythril `compile_solidity`:

* doesn't use its own `solc_binary` argument
* doesn't offer NIX signal tracking if `solc` has internal fatal issues,
such as SIGSEGV

This commit adds a more verbose message for a fatal error in `solc` and
uses the `solc_binary` argument.

b-mueller/mythril,b-mueller/mythril,b-mueller/mythril,b-mueller/mythril