This patch adds a preprocessor that can expand nested for-loops for
saving some copy-n-paste in *.td files.
The preprocessor is not yet integrated with TGParser, and so it has
no direct effect on *.td inputs. However, you may preprocess an td
input (and only preprocess it).
To test the proprecessor, type:
tblgen -E -o $@ $<
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141079 91177308-0d34-0410-b5e6-96231b3b80d8