Fix bogus regexp test.

Fix bogus regexp test.

The reason this test fails on ARM hardware but not on Intel hardware
(including the ARM simulator) is this:
'\xa0' is interpreted as a negative signed byte number. Casting it to
uc16 sign-extends it. The resulting string does not fit into a one-byte
string, thus a two-byte string is allocated.
For some reason the code compiled for ARM does not sign-extend, and 0xa0
fits into a one-byte string. Thus a one-byte string is allocated. Trying
to cast it to two-byte causes assertion failure.


BUG=

Committed: https://code.google.com/p/v8/source/detail?r=13729

[drcarney, 2013-02-26 10:48:56]

lgtm

[Yang, 2013-02-26 10:50:05]

Committed patchset #1 manually as r13729 (presubmit successful).