[builtins] Omit 80-bit builtins on Android and MSVC

long double is a 64-bit double-precision type on:
 - MSVC (32- and 64-bit x86)
 - Android (32-bit x86)

long double is a 128-bit quad-precision type on x86_64 Android.

The assembly variants of the 80-bit builtins are correct, but some of
the builtins are implemented in C and require that long double be the
80-bit type passed via an x87 register.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D82153