Do not typedef char16_t if it is a keyword.

Don't define char16_t on platforms where char16_t is a keyword, as
C11 and C++11 define it to be.

Change-Id: I6717bc2133c1363ecd85861f3869e1eabd2ce96a

include/cutils/jstring.h

@@ -24,7 +24,10 @@
 extern "C" {
 #endif
 
-typedef uint16_t char16_t;
+#if __STDC_VERSION__ < 201112L && __cplusplus < 201103L
+  typedef uint16_t char16_t;
+#endif
+  // otherwise char16_t is a keyword with the right semantics
 
 extern char * strndup16to8 (const char16_t* s, size_t n);
 extern size_t strnlen16to8 (const char16_t* s, size_t n);