Implement wctomb(3) for ltrace.

This is an implementation in the style of the rest: char == byte.

We might want to come back and implement UTF-8, but this is enough for ltrace.

Bug: 13747066
Change-Id: Ib2b63609c9014fdef9a8491e067467c4fc5ae3cc

libc/include/stdlib.h

@@ -151,7 +151,6 @@ extern lldiv_t   lldiv(long long, long long);
 extern const char* getprogname(void);
 extern void setprogname(const char*);
 
-#if 1 /* MISSING FROM BIONIC - ENABLED FOR STLPort and libstdc++-v3 */
 /* make STLPort happy */
 extern int      mblen(const char *, size_t);
 extern size_t   mbstowcs(wchar_t *, const char *, size_t);
@@ -160,7 +159,6 @@ extern int      mbtowc(wchar_t *, const char *, size_t);
 /* Likewise, make libstdc++-v3 happy.  */
 extern int	wctomb(char *, wchar_t);
 extern size_t	wcstombs(char *, const wchar_t *, size_t);
-#endif /* MISSING */
 
 #define MB_CUR_MAX 1