feat: Allow tox_ prefixes for custom attributes.

This is needed if we ever want to annotate the public API with these
attributes.

src/Language/Cimple/Lexer.x

@@ -151,7 +151,11 @@ tokens :-
 <0>		"#define"				{ mkL PpDefine `andBegin` ppSC }
 <0>		"#undef"				{ mkL PpUndef }
 <0>		"#include"				{ mkL PpInclude }
-<0,ppSC>	"bitwise"				{ mkL KwBitwise }
+<0,ppSC>	"tox_"?"bitwise"			{ mkL KwBitwise }
+<0,ppSC>	"tox_"?"force"				{ mkL KwForce }
+<0,ppSC>	"tox_"?"non_null"			{ mkL KwNonNull }
+<0,ppSC>	"tox_"?"nullable"			{ mkL KwNullable }
+<0,ppSC>	"tox_"?"owner"				{ mkL KwOwner }
 <0,ppSC>	"break"					{ mkL KwBreak }
 <0,ppSC>	"case"					{ mkL KwCase }
 <0,ppSC>	"const"					{ mkL KwConst }
@@ -162,12 +166,8 @@ tokens :-
 <0,ppSC>	"enum"					{ mkL KwEnum }
 <0,ppSC>	"extern"				{ mkL KwExtern }
 <0,ppSC>	"for"					{ mkL KwFor }
-<0,ppSC>	"force"					{ mkL KwForce }
 <0,ppSC>	"goto"					{ mkL KwGoto }
 <0,ppSC>	"if"					{ mkL KwIf }
-<0,ppSC>	"non_null"				{ mkL KwNonNull }
-<0,ppSC>	"nullable"				{ mkL KwNullable }
-<0,ppSC>	"owner"					{ mkL KwOwner }
 <0,ppSC>	"return"				{ mkL KwReturn }
 <0,ppSC>	"sizeof"				{ mkL KwSizeof }
 <0,ppSC>	"static"				{ mkL KwStatic }