Fails to build with Clang 10

[Alexey Dokuchaev]

Hi,

Recently FreeBSD switched its default compiler to Clang, and now GNU APL
v1.8 does not build due to this:

  ...
  NumericCell.cc:1405:27: error: implicit conversion from 'long long' to
  'double' changes value from 9223372036854775807 to 9223372036854775808
  [-Werror,-Wimplicit-int-float-conversion]
     if (is_float_cell() && 0x7FFFFFFFFFFFFFFFLL < get_real_value())
                            ^~~~~~~~~~~~~~~~~~~~ ~
  1 error generated.

Any idea how to properly fix this?

./danfe