Fix llvm-extract's "writing bitcode to a terminal" warning, which wasn't

working. To support this, add an is_displayed() function to raw_ostream,
and generalize Process::StandardOutIsDisplayed and friends in order to
support it.

Also, call RemoveFileOnSignal before creating a file instead of after, so
that the file isn't left behind if the program is interrupted between when
the file is created and RemoveFileOnSignal is called.

While here, add a -S to llvm-extract and port it to IRReader so that it
supports assembly input.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81568 91177308-0d34-0410-b5e6-96231b3b80d8

lib/System/Unix/Process.inc

@@ -179,26 +179,20 @@ void Process::PreventCoreFiles() {
 }
 
 bool Process::StandardInIsUserInput() {
-#if HAVE_ISATTY
-  return isatty(0);
-#else
-  // If we don't have isatty, just return false.
-  return false;
-#endif
+  return FileDescriptorIsDisplayed(STDIN_FILENO);
 }
 
 bool Process::StandardOutIsDisplayed() {
-#if HAVE_ISATTY
-  return isatty(1);
-#else
-  // If we don't have isatty, just return false.
-  return false;
-#endif
+  return FileDescriptorIsDisplayed(STDOUT_FILENO);
 }
 
 bool Process::StandardErrIsDisplayed() {
+  return FileDescriptorIsDisplayed(STDERR_FILENO);
+}
+
+bool Process::FileDescriptorIsDisplayed(int fd) {
 #if HAVE_ISATTY
-  return isatty(2);
+  return isatty(fd);
 #else
   // If we don't have isatty, just return false.
   return false;