[PATCH] [MC] Make bundle alignment mode setting idempotent and support nested bundles

[Jan Voung]

otherwise LGTM too

================
Comment at: lib/MC/MCELFStreamer.cpp:483
@@ -479,3 +482,3 @@
   else
-    report_fatal_error(".bundle_align_mode should be only set once per file");
+    report_fatal_error(".bundle_align_mode cannot be changed once set");
 }
----------------
Would be good add a test that the error is thrown when the align modes are changed.

================
Comment at: test/MC/X86/AlignedBundling/nesting.s:11
@@ +10,3 @@
+  .bundle_align_mode 4
+# Each of these callq isntructions is 5 bytes long
+  callq bar
----------------
isntructions -> instructions

================
Comment at: test/MC/X86/AlignedBundling/nesting.s:56
@@ +55,3 @@
+quux:
+# Each of these callq isntructions is 5 bytes long
+  callq bar
----------------
No need to say callq is 5 bytes long here too (already stated earlier)

http://reviews.llvm.org/D5801