swift234

[stdlib] bitwise assignments for NS_OPTIONS

Fixes <rdar://problem/17797711>

This is rather a kluge because of two other problems.  Having these
fixed would allow a cleaner solution:

<rdar://problem/17815538> synthesize an allZeros static var for
BitwiseOperationsType conformance of imported NS_OPTIONS

<rdar://problem/17815767> Adding three overloads to stdlib slows
Fibonacci by 18-19%

Swift SVN r20563