driconf: Add a new option: disable_glsl_line_continuations

driconf: Add a new option: disable_glsl_line_continuations

This is to enable a quirk for Savage2 which includes a shader with a stray '\'
at the end of a comment line. Interpreting that backslash as a line
continuation will break the compilation of the shader, so we need a way to
disable this.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>