always aligned to a 16 byte (or higher) boundary will now only be aligned to an 8
  byte boundary.
  Some programs that use assembly instructions that require memory addresses to be
  more than 8-byte aligned and rely on the memory allocator's previous alignment behavior
  may break, but we expect such programs to be rare.
  Such programs may be built with <code>GOEXPERIMENT=noallocheaders</code> to revert