tccasm: make VT_VOID symbols ST_NOTYPE, elf-wise

This was confusing objdump such that it did not print
disassembly with -d.

Also, put filename as with C compilation

libtcc.c

@@ -780,6 +780,8 @@ static void put_extern_sym2(Sym *sym, Section *section,
         if (FUNC_CALL(attr) == FUNC_STDCALL)
             other |= 2;
 #endif
+    } else if ((sym->type.t & VT_BTYPE) == VT_VOID) {
+        sym_type = STT_NOTYPE;
     } else {
         sym_type = STT_OBJECT;
     }

tccasm.c

@@ -712,6 +712,12 @@ static int tcc_assemble(TCCState *s1, int do_preprocess)
 
     define_start = define_stack;
 
+    /* an elf symbol of type STT_FILE must be put so that STB_LOCAL
+       symbols can be safely used */
+    put_elf_sym(symtab_section, 0, 0,
+                ELFW(ST_INFO)(STB_LOCAL, STT_FILE), 0,
+                SHN_ABS, file->filename);
+
     ret = tcc_assemble_internal(s1, do_preprocess);
 
     cur_text_section->data_offset = ind;