PR19598: Provide the ability to RAUW a declaration with itself, creating a non-temporary copy and using that to RAUW.

Also, provide the ability to create temporary and non-temporary
declarations, as not all declarations may be replaced by definitions
later on.

This provides the necessary infrastructure for Clang to fix PR19598,
leaking temporary MDNodes in Clang's debug info generation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208054 91177308-0d34-0410-b5e6-96231b3b80d8
[Build] Add rule to generate fully-expanded .td file

I found it useful in the past and now again to have a version of the .td file
where all the records are expanded.  This adds a makefile rule to generate
this on demand.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208056 91177308-0d34-0410-b5e6-96231b3b80d8