swift234

SILOptimizer: Fixes for non-fragile references in fragile functions

Two fixes to optimization passes to maintain restrictions about what
[fragile] functions can reference:

- When devirtualizing witness methods, don't devirtualize if the caller
  is fragile and the callee is not. This matches existing logic in
  class devirtualization.

- When performing generic or function signature specialization, don't
  specialize non-fragile functions referenced from fragile functions.

Since @_transparent functions are allowed to call 'static inline'
imported functions, also be sure to mark the foreign-to-native thunk
for such a function as [fragile].

With this patch, the standard library and performance test suite
now build with -enable-resilience.

No new tests for this stuff here -- the existing tests together
with an -enable-resilience build provide coverage.

Closes out <https://bugs.swift.org/browse/SR-267> and
<https://bugs.swift.org/browse/SR-268>.