gcc's -fstrict-aliasing is biting us when we use the stack to store
different types of objects.  For example:

  *((StgDouble*)((W_)Sp-8)) = *((StgDouble*)((W_)Sp+8));
  Sp[1] = (W_)&s1Cx_info;

gcc feels free to reorder these two lines, because they refer to
differently typed objects, even though the assignment to Sp[1] clearly
aliases the read from the same location.

Trying to fix this by accessing locations using union types might be
possible, but I took the sledgehammer approach of
-fno-strict-aliasing.  This is justified to a certain extent because
our generated C code is derived from a very weakly-typed internal
language (C--).