-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.

tcc-doc.texi

@@ -241,6 +241,9 @@ Allow a MS C compiler extensions to the language. Curretly this
 assume a nested named structure declaration without identifier behave
 like an unnamed one.
 
+@item -fdollars-in-identifiers
+Allow a dollars in identifiers
+
 @end table
 
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