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
diff --git a/libc/bionic/wchar.cpp b/libc/bionic/wchar.cpp
index 50a3875..8d56458 100644
--- a/libc/bionic/wchar.cpp
+++ b/libc/bionic/wchar.cpp
@@ -28,6 +28,7 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #include <wchar.h>
@@ -156,8 +157,8 @@
   return 1;
 }
 
-size_t mbrlen(const char* /*s*/, size_t n, mbstate_t* /*ps*/) {
-  return (n != 0);
+size_t mbrlen(const char* s, size_t n, mbstate_t* /*ps*/) {
+  return (n == 0 || s[0] == 0) ? 0 : 1;
 }
 
 size_t mbrtowc(wchar_t* pwc, const char* s, size_t n, mbstate_t* /*ps*/) {
@@ -217,13 +218,26 @@
   return ungetc(static_cast<char>(wc), stream);
 }
 
-size_t wcrtomb(char* s, wchar_t /*wc*/, mbstate_t* /*ps*/) {
-  if (s != NULL) {
-    *s = 1;
+int wctomb(char* s, wchar_t wc) {
+  if (s == NULL) {
+    return 0;
+  }
+  if (wc <= 0xff) {
+    *s = static_cast<char>(wc);
+  } else {
+    *s = '?';
   }
   return 1;
 }
 
+size_t wcrtomb(char* s, wchar_t wc, mbstate_t* /*ps*/) {
+  if (s == NULL) {
+    char buf[MB_LEN_MAX];
+    return wctomb(buf, L'\0');
+  }
+  return wctomb(s, wc);
+}
+
 size_t wcsftime(wchar_t* wcs, size_t maxsize, const wchar_t* format,  const struct tm* timptr) {
   return strftime(reinterpret_cast<char*>(wcs), maxsize, reinterpret_cast<const char*>(format), timptr);
 }
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 9b7e6d1..5dbcb3d 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -151,7 +151,6 @@
 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 @@
 /* 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
 
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 32cf127..89c6fb6 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -36,13 +36,6 @@
 #include <time.h>
 #include <malloc.h>
 
-/* IMPORTANT: Any code that relies on wide character support is essentially
- *            non-portable and/or broken. the only reason this header exist
- *            is because I'm really a nice guy. However, I'm not nice enough
- *            to provide you with a real implementation. instead wchar_t == char
- *            and all wc functions are stubs to their "normal" equivalent...
- */
-
 __BEGIN_DECLS
 
 typedef __WINT_TYPE__           wint_t;
@@ -150,12 +143,11 @@
 extern size_t wcslcat(wchar_t*, const wchar_t*, size_t);
 extern size_t wcslcpy(wchar_t*, const wchar_t*, size_t);
 
-/* No really supported.  These are just for making libstdc++-v3 happy.  */
 typedef void *wctrans_t;
-extern wint_t		 towctrans(wint_t, wctrans_t);
-extern wctrans_t	 wctrans (const char *);
+extern wint_t towctrans(wint_t, wctrans_t);
+extern wctrans_t wctrans(const char*);
 
-#if _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
+#if __POSIX_VISIBLE >= 200809
 wchar_t* wcsdup(const wchar_t*);
 size_t wcsnlen(const wchar_t*, size_t);
 #endif