[+0-all-args] When diagnosing closure escapes, look through sil borrows.

[gottesmm]

I also added an option called sil-assert-on-exclusivity-failure that causes the
optimizer to assert if an exclusivity failure is hit. This enables quicker
debugging of exclusivity violations since at the assertion point, you drop
straight down into the debugger. This is only enabled with asserts.

rdar://34222540

[gottesmm]

@swift-ci smoke test and merge

[gottesmm]

@swift-ci smoke test and merge

[atrick]

Thanks. This looks fine for now. Just a couple comments..

• I'm not sure we we would ever need to borrow a noescape closure, but hopefully it's harmless for now.
• I would much prefer a general debugging flag--just one flag to remember to always turn on in lldb--that always asserts at diagnostic errors, fatal errors, etc.

[gottesmm]

@atrick I agree on both points.