Fix inlining loops in OSR mode.

When compiling a method in OSR mode and the method does not
contain a loop (arguably, a very odd case) but we inline
another method with a loop and then the final DCE re-runs
the loop identification, the inlined loop would previously
be marked as irreducible. However, the SSA liveness analysis
expects irreducible loop to have extra loop Phis which were
already eliminated from the loop before the inner graph was
inlined to the outer graph, so we would fail a DCHECK().

We fix this by not marking inlined loops as irreducible when
compiling in OSR mode.

Bug: 28210356

(cherry picked from commit fd66c50d)

Change-Id: I149273b766d1c713c571baad6033c5f70e6dd960