tweak symbolizer max-expected-frame-size for 32-bit

Summary:
Avoids:
```
folly/experimental/symbolizer/StackTrace.cpp:192:15: error: the pointer incremented by 68719476736 refers past the last possible element for an array in 32-bit address space containing 64-bit (8-byte) elements (max possible 536870912 elements) [-Werror,-Warray-bounds]
              normalStackFrame + kMaxExpectedStackFrameSize)) {
              ^                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Reviewed By: kennyyu, luciang

Differential Revision: D33837703

fbshipit-source-id: 0ca6b7ba6c2f76d0be3c54c9784c305125b525df

folly/experimental/symbolizer/StackTrace.cpp

@@ -70,7 +70,12 @@ namespace {
 
 // Heuristic for guessing the maximum stack frame size. This is needed to ensure
 // we do not have stack corruption while walking the stack.
-constexpr uint64_t kMaxExpectedStackFrameSize = 0x1000000000;
+constexpr size_t kMaxExpectedStackFrameSizeLg2 = sizeof(size_t) == 8
+    ? 36 // 64GB
+    : 28 // 256MB
+    ;
+constexpr size_t kMaxExpectedStackFrameSize //
+    = size_t(1) << kMaxExpectedStackFrameSizeLg2;
 
 #if FOLLY_HAVE_LIBUNWIND