-fdollar-in-identifiers switch which enables '$' in identifiers

library Cello: http://libcello.org/ which uses `$` and several
    variations of as macros.

    There is also RayLanguage which also uses it as a macro for a kind of
    ObjC style message passing: https://github.com/kojiba/RayLanguage

    This is a patch from Daniel Holden.

libtcc.c

@@ -1482,6 +1482,7 @@ static const FlagDef flag_defs[] = {
     { offsetof(TCCState, leading_underscore), 0, "leading-underscore" },
     { offsetof(TCCState, ms_extensions), 0, "ms-extensions" },
     { offsetof(TCCState, old_struct_init_code), 0, "old-struct-init-code" },
+    { offsetof(TCCState, dollars_in_identifiers), 0, "dollars-in-identifiers" },
 };
 
 /* set/reset a flag */