Use default alignment if alignof(std::max_align_t) < 16 with C++11.

- As per Andrew Hunter’s comments in the commit which added Jet
  alignment when using C++11 here:
  https://ceres-solver-review.googlesource.com/#/c/7100, there is wide
  lattitude in the standard about what the maximum supported alignment
  can be.
- Previously, we were forcing the alignment to 1, if the value of
  alignof(std::max_align_t), which we use as a proxy for the maximum
  supported alignment on the platform, was < 16.
- An alignment of 1 is not valid for Jets, as it would weaken the
  natural alignment of the types within a Jet, which would typically be
  4 (32-bit systems) or 8 (64-bit systems), thus resulting in a compiler
  error.
- This was reported as issue 235 for Clang 3.8 on i386:
  https://github.com/ceres-solver/ceres-solver/issues/235.

Change-Id: Ie39e5499c64f9231f29ebf4392992b5c9ce2e385