Fixes #4093

Added COMMA macro to nimbase.h,
changed code generation for c++ template types to insert COMMA im
between the arguments, instead of ",".

compiler/ccgtypes.nim

@@ -654,7 +654,7 @@ proc getTypeDescAux(m: BModule, typ: PType, check: var IntSet): Rope =
       else:
         result = cppName & "<"
         for i in 1 .. typ.len-2:
-          if i > 1: result.add(", ")
+          if i > 1: result.add(" COMMA ")
           result.add(getTypeDescAux(m, typ.sons[i], check))
         result.add("> ")
       # always call for sideeffects:

lib/nimbase.h

@@ -222,6 +222,8 @@ __clang__
 
 /* ----------------------------------------------------------------------- */
 
+#define COMMA ,
+
 #include <limits.h>
 #include <stddef.h>