fasm: patch ignored runtime dependency warnings

[jleightcap]

see:
ngi-nix/ngipkgs#7 (comment)

fasm provides two options for runtime parsing: textx and ANTLR4.

ANTLR4 is:

• not immediately in nixpkgs as a C++ runtime with compatible CMake
  hooks
• not easily exposed in the fasm build scripts.

There is an Arch Linux specific workaround on an unmerged branch.

For the time being, fall back to the flower textx parser and patch out
the runtime warning:

RuntimeWarning: Unable to import fast Antlr4 parser implementation.
      ImportError: cannot import name tags

      Falling back to the much slower pure Python textX based parser
      implementation.

      Getting the faster antlr parser can normally be done by installing the
      required dependencies and then reinstalling the fasm package with:
        pip uninstall
        pip install -v fasm

      warn(

Thanks for the tip @fricklerhandwerk!

Signed-off-by: Jack Leightcap jack@leightcap.com