Add a paste operator '#' to take two identifier-like strings and joint
them. Internally paste gets represented as a !strconcat() with any
necessary casts to string added.
This will be used to implement basic for loop functionality as in:
for i = [0, 1, 2, 3, 4, 5, 6, 7] {
def R#i : Register<...>
}
llvm-svn: 142525