Fix floating point number comparisons in testsuite/libffi.call/float[123].c.

Rewrite the checks for approximate equality of floating point return
values to be in the form "fabs(a - b) < EPS" instead of just
"a - b < EPS".
Take a float absolute value using fabs() instead of abs().

Replace integer abs() by floating point fabs() in the approximate
equality check for float values.
Merge pull request #144 from atrosinenko/testsuite-fp-comparison-fix

Floating point number comparison fix for testsuite