xtensa: snapshot

Almost all tests run now, except:
* C++ tests (no working compiler right now)
* promotion (too slow on the test board, dejagnu times out)
* err_bad_abi (xtensa simply asserts)
* va_1.c (unaligned exception in the test code, unrelated to xtensa implement.)

Signed-off-by: Chris Zankel <chris@zankel.net>