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=

Review URL: https://chromiumcodereview.appspot.com/12319111

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13729 ce2b1a6d-e550-0410-aec6-3dcde31c8c00