Changed multi-line C comments into another style.

The left side doesn't look unbalanced.

src/ld65/extsyms.h

@@ -69,16 +69,16 @@ void FreeExtSymTab (ExtSymTab* Tab);
 
 ExtSym* GetExtSym (const ExtSymTab* Tab, unsigned Name);
 /* Return the entry for the external symbol with the given name. Return NULL
- * if there is no such symbol.
- */
+** if there is no such symbol.
+*/
 
 unsigned ExtSymCount (const ExtSymTab* Tab);
 /* Return the number of symbols in the table */
 
 const ExtSym* ExtSymList (const ExtSymTab* Tab);
 /* Return the start of the symbol list sorted by symbol number. Call
- * ExtSymNext for the next symbol.
- */
+** ExtSymNext for the next symbol.
+*/
 
 unsigned ExtSymNum (const ExtSym* E);
 /* Return the number of an external symbol */