When printing MIR, output to errs() rather than outs().

Summary:
Without this, this command

  $ llvm-run llc -stop-after machine-cp -o - <( echo '' )

outputs an error, because we close stdout twice -- once when closing the
file opened for "-o", and again when closing outs().

Also clarify in the outs() definition that you can't ever call it if you
want to open your own raw_fd_ostream on stdout.

Reviewers: jroelofs, tstellarAMD

Subscribers: jholewinski, qcolombet, dsanders, llvm-commits

Differential Revision: http://reviews.llvm.org/D17422

llvm-svn: 261286
diff --git a/llvm/test/DebugInfo/X86/bbjoin.ll b/llvm/test/DebugInfo/X86/bbjoin.ll
index 385cb6c..fea7491 100644
--- a/llvm/test/DebugInfo/X86/bbjoin.ll
+++ b/llvm/test/DebugInfo/X86/bbjoin.ll
@@ -1,5 +1,5 @@
 ; RUN: llc -mtriple=x86_64-apple-macosx10.9.0 %s -stop-after=livedebugvars \
-; RUN:   -o %t.s | FileCheck %s
+; RUN:   -o %t.s 2>&1 | FileCheck %s
 ; Generated from:
 ; void g(int *);
 ; int f() {