[AIX]Emit function descriptor csect in assembly

This patch emits the function descriptor csect for functions with definitions
under both 32-bit/64-bit mode on AIX.

Differential Revision: https://reviews.llvm.org/D66724

llvm-svn: 373009
diff --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index 816e742..e411e24 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -277,6 +277,9 @@
 
   case MCSA_AltEntry:
     llvm_unreachable("ELF doesn't support the .alt_entry attribute");
+
+  case MCSA_LGlobal:
+    llvm_unreachable("ELF doesn't support the .lglobl attribute");
   }
 
   return true;