-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.

tccpp.c

@@ -2286,7 +2286,10 @@ maybe_newline:
             }
         }
         break;
-
+    
+    /* treat $ as allowed char in indentifier  */
+    case '$': if (!tcc_state->dollars_in_identifiers) goto parse_simple;    
+    
     case 'a': case 'b': case 'c': case 'd':
     case 'e': case 'f': case 'g': case 'h':
     case 'i': case 'j': case 'k': case 'l':
@@ -2589,8 +2592,8 @@ maybe_newline:
     case ':':
     case '?':
     case '~':
-    case '$': /* only used in assembler */
-    case '@': /* dito */
+    case '@': /* only used in assembler */
+    parse_simple:
         tok = c;
         p++;
         break;
@@ -3174,7 +3177,8 @@ ST_FUNC void preprocess_new(void)
 
     /* init isid table */
     for(i=CH_EOF;i<256;i++)
-        isidnum_table[i-CH_EOF] = isid(i) || isnum(i);
+        isidnum_table[i-CH_EOF] = (isid(i) || isnum(i) ||
+            (tcc_state->dollars_in_identifiers ? i == '$' : 0));
 
     /* add all tokens */
     if (table_ident) {