Fixes an issue where two types can collide in the cgen

When generating a header with `--header` and then using it from another Nim project to import the generated types, generic instances can collide and produce an error i.e. `typedef MyGeneric[TypeA] typename` `typedef MyGeneric[TypeB] typename` `signature` here cant be the same as they are different types.  This issue can be avoided by using the Nim type as part of the name which is what PR does.

compiler/ccgtypes.nim

@@ -1114,7 +1114,7 @@ proc getTypeDescAux(m: BModule; origTyp: PType, check: var IntSet; kind: TypeDes
       # The resulting type will include commas and these won't play well
       # with the C macros for defining procs such as N_NIMCALL. We must
       # create a typedef for the type and use it in the proc signature:
-      let typedefName = "TY" & $sig
+      let typedefName = "TY$1_$2" % [$sig, m.encodeType(origTyp)]
       m.s[cfsTypes].addf("typedef $1 $2;$n", [result, typedefName])
       m.typeCache[sig] = typedefName
       result = typedefName