Fix test failure with 374562 on Hexagon

__builtin_assume_aligned takes a size_t which is a 32 bit int on
hexagon.  Thus, the constant gets converted to a 32 bit value, resulting
in 0 not being a power of 2.  This patch changes the constant being
passed to 2**30 so that it fails, but doesnt exceed 30 bits.

llvm-svn: 374569