LTO: introduce object file-based on-disk module format.

This format is simply a regular object file with the bitcode stored in a
section named ".llvmbc", plus any number of other (non-allocated) sections.

One immediate use case for this is to accommodate compilation processes
which expect the object file to contain metadata in non-allocated sections,
such as the ".go_export" section used by some Go compilers [1], although I
imagine that in the future we could consider compiling parts of the module
(such as large non-inlinable functions) directly into the object file to
improve LTO efficiency.

[1] http://golang.org/doc/install/gccgo#Imports

Differential Revision: http://reviews.llvm.org/D4371

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218078 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/Error.h

@@ -26,7 +26,8 @@ enum class object_error {
   arch_not_found,
   invalid_file_type,
   parse_failed,
-  unexpected_eof
+  unexpected_eof,
+  bitcode_section_not_found,
 };
 
 inline std::error_code make_error_code(object_error e) {