When we load a function or method body from an AST file, we check

When we load a function or method body from an AST file, we check
whether that function/method already has a body (loaded from some
other AST file), as introduced in r165137. Delay this check until
after the redeclaration chains have been wired up.

While I'm here, make the loading of method bodies lazy.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165513 91177308-0d34-0410-b5e6-96231b3b80d8