[libFuzzer] don't change sanitizer_report_fd for fuchsia.

[charco]

Summary

This commit modifies the DupAndCloseStderr function in FuzzerIO.cpp,
adding an if-macro to exclude calling sanitizer_set_report in fuchsia.

Fuchsia does not have support for that function and if it is called, the
program will crash because it is unimplemented.

Discarding the sanitizer reports from stderr is not an issue because
they are also being logged to the console and are available via `fx
syslog`.

[phosek]

compiler-rt/lib/fuzzer/FuzzerIO.cpp

119

Can you indent the comment so it starts on the same column as the rest of this block?

120

I'd omit the second sentence, fx syslog is an internal detail of Fuchsia development workflow and is irrelevant here.

compiler-rt/lib/fuzzer/FuzzerIO.cpp

 }
 
 void DupAndCloseStderr() {
   int OutputFd = DuplicateFile(2);
   if (OutputFd > 0) {
     FILE *NewOutputFile = OpenFile(OutputFd, "w");
     if (NewOutputFile) {
       OutputFile = NewOutputFile;
+#if !LIBFUZZER_FUCHSIA
+// Fuchsia does not support redirecting clang's reports to a file descriptor.
+// These reports are also logged to the console and show up via fx syslog so
+// it's not important if they are not in the fuzzer output.
       if (EF->__sanitizer_set_report_fd)
         EF->__sanitizer_set_report_fd(
             reinterpret_cast<void *>(GetHandleFromFd(OutputFd)));
+#endif
       DiscardOutput(2);
     }
   }
 }
 
 void CloseStdout() {
   DiscardOutput(1);
 }