Update i386 & armv7 minimum iOS version to 7.0

iOS 5 (and any below 7.1) is deprecated. Apple doesn't distribute the supporting libraries for this platform anymore as of Xcode 6, so it causes a linker error.
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 #143 from adamkaplan/patch-1

Update i386 & armv7 minimum iOS version to 7.0
Merge pull request #144 from atrosinenko/testsuite-fp-comparison-fix

Floating point number comparison fix for testsuite
Merge pull request #145 from rth7680/master

Configure and testsuite cleanups, v2