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

docs/CommandGuide/llvm-extract.pod

@@ -45,6 +45,10 @@ Print a summary of command line options.
 Specify the output filename.  If filename is "-" (the default), then
 B<llvm-extract> sends its output to standard output.
 
+=item B<-S>
+
+Write output in LLVM intermediate language (instead of bitcode).
+
 =back
 
 =head1 EXIT STATUS