Increase the amount of memory we allow the constraint solver to use.

Various changes throughout the compiler and libraries appear to have
resulted in an increase in memory usage in the constraint solver since
Swift 2.2.

This is a stop-gap measure to allow more expressions to compile while
the expression type checker is being improved.

We've seen several cases where even a modest increase allows things that
compiled with Swift 2.2 to continue to compile (albeit with generally
longer compile times).

(cherry picked from commit 8886f77)

Author: rudkx

include/swift/Basic/LangOptions.h

@@ -131,7 +131,7 @@ namespace swift {
 
     /// \brief The upper bound, in bytes, of temporary data that can be
     /// allocated by the constraint solver.
-    unsigned SolverMemoryThreshold = 15000000;
+    unsigned SolverMemoryThreshold = 33554432; /* 32 * 1024 * 1024 */
 
     /// \brief Perform all dynamic allocations using malloc/free instead of
     /// optimized custom allocator, so that memory debugging tools can be used.