This implements support for 130 of the 132 x87 ops as interpreter
fallbacks.
The two missing ops are the BCD load and BCD store instructions and can
be implemented another time.
This allows us to no longer have to rely on a libstdc++ modification to
handle their usage of long double. This instead works entirely through
using `long double` directly in the interpreter. Which will either use
real x87 on an x86 host. Or in the case of ARM devices, fall down
glibc's long double soft float path.
This doesn't necessarily need to be quick right now. It's more important
to have the compatibility improvement from this.
Stefanos Kornilios Mitsis Poiitidis