cosl test failure

[Bruno Haible]

Hi Paolo,

I added trivial tests for the mathl functions, that verify that
  1) there are no link errors,
  2) on a randomly picked value, the function's result is correct
     to 10 decimal digits.

For the cosl() function, when compiled from the gnulib sources, this
test fails. Seen on OpenBSD/x86, Solaris/SPARC, Cygwin. gdb shows this:

  Breakpoint 1, main () at test-cosl.c:40
  40        ASSERT (y >= 0.8253356149L && y <= 0.8253356150L);
  (gdb) print y
  $1 = 0.82533762773239849330764172918861732

It seems that the result has an accuracy of only 6 decimal digits,
i.e. 'float' precision, only!

Bruno