[libc++] Un-guarded reference to uncaught_exception() in ostream header

[rmaprath]

Summary

The ostream header contains an un-guarded reference to uncaught_exception() which causes it to drag in the exception handling machinery even when not required (i.e. when compiling with -fno-exceptions). There are no tests for this fix as the behaviour is only visible at link time (unnecessary symbols present and increased image size).

[rmaprath]

Updated patch with bit more context (-U20).

[rmaprath]

Gentle ping.

include/ostream

 basic_ostream<_CharT, _Traits>::sentry::~sentry()
 {
     if (__os_.rdbuf() && __os_.good() && (__os_.flags() & ios_base::unitbuf)
-                      && !uncaught_exception())
+#ifndef _LIBCPP_NO_EXCEPTIONS
+                      && !uncaught_exception()
+#endif  // _LIBCPP_NO_EXCEPTIONS
+       )
     {
 #ifndef _LIBCPP_NO_EXCEPTIONS
         try