ARM JIT: fix test for VFP

Having `__VFP_FP__` defined does not mean that VFP instructions are
available; it just means that floating-point is native-endian.

According to

 https://wiki.debian.org/ArmEabiPort

the absence of `__SOFTFP__` combined with the precense of `__VFP_FP__`
can mean VFP, though.