Revert "Simplify switching floating-point exception handlers"

This reverts commit 392d94e39831c52e5974c7a12ca951d62c594009.
Revert "Add some exception handling for interrupts and floating-point exceptions"

This reverts commit 4651a4b3729fdb1d136eb83feaae4b66e84fd56b.
Add -O3 to compilation args