scriptcomp: Support #line directive

[mtijanic]

The #line <line_number> <filename> directive is emitted by many preprocessors as a way to tell the next stage compiler which un-preprocessed line a certain source line refers to.
Consider:

1  #if 0
2  // deadcode
3  #endif
4  compile_error_here

After preprocessing with cpp(1), line 4 becomes line 1, and then if that is fed into nwn_script_comp, it'll report an error at an incorrect line.
Most preprocessors have a way to emit code like this

#line 1
compile_error_here

which would make the compiler report correct lines. This makes it easier to hook any preprocessor as a build step prior to calling the compiler.