Add "custom build parameters" option for code files

Compilers like sdcc has many commandline options to control how to compile a source file.

For example, if you want to compiler code for z80, option "-mz80" is needed.

So my request is to add an option in the settings for code file, it will be autoed added to the command while compiling.

I've made a demo patch. I don't know if other compilers need custom options, so it only works with sdcc:

Yes, that's a nice (and needed) feature.

Patch applied at Rev 1890.

I did some minor changes:
- Property added to Compiler settings instead to File settings.
- Named "Extra build arguments" instead of "Custom build arguments", to indicate that this is added to default arguments, not substituting default arguments.