Use a larger C++ stack in asan builds

Summary: asan builds use a lot more C++ stack in certain functions than normal
builds (40-50x more in some cases). This is a problem for some of our recursive
cfg traversal functions in the jit. A better fix would be to not recurse over
data structures that are sized by user code, but making the C++ stack bigger
will allow us to reenable the automated asan builds without rewriting a bunch
of things.

Reviewed By: @jdelong

Differential Revision: D1573383
Fix remaining asan test failures

Summary: - The JEWISH_MONTH_NAME macro was accessing an array out of bounds when given a
  year < 1. According to a few sources on the internet, years < 1 don't exist
  in the Jewish calendar, so the result is undefined.
- A copy of ext/gmp/tests/002.php already exists in test/slow, so instead of
  applying the same fix I moved it to flaky.

Reviewed By: @alexmalyshev, @bertmaher

Differential Revision: D1573700