Add the start of the support for llvm-objdump’s -private-headers for Mach-O files.

This adds the printing of the mach header. Load command printing will be next.

llvm-svn: 216285
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
index 0074271..259d001 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -834,6 +834,8 @@
     printELFFileHeader(o);
   } else if (o->isCOFF()) {
     printCOFFFileHeader(o);
+  } else if (o->isMachO()) {
+    printMachOFileHeader(o);
   }
 }