util/driconf: add new ignore_write_to_readonly_var workaround

This forces the GLSL compiler to ignore writes to readonly vars
rather than throwing an error.

Cc: mesa-stable

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11602>

src/compiler/glsl/glsl_parser_extras.cpp

@@ -321,6 +321,8 @@ _mesa_glsl_parse_state::_mesa_glsl_parse_state(struct gl_context *_ctx,
       ctx->Const.AllowGLSL120SubsetIn110;
    this->allow_builtin_variable_redeclaration =
       ctx->Const.AllowGLSLBuiltinVariableRedeclaration;
+   this->ignore_write_to_readonly_var =
+      ctx->Const.GLSLIgnoreWriteToReadonlyVar;
 
    this->cs_input_local_size_variable_specified = false;