Operations not available on ARMv6-M targets

[japaric]

These operations are not available on the thumbv6m-none-eabi target:

• f64 as i64
• f64 as u64
• f64 == f64
• f64 > f64
• f64 < f64
• f32 as i64
• f32 as u64
• f32 == f32
• f32 > f32
• f32 < f32

and won't be available until these intrinsics:

• __aeabi_dcmpeq
• __aeabi_dcmpgt
• __aeabi_dcmple
• __aeabi_dcmplt
• __aeabi_fcmpeq
• __aeabi_fcmpgt
• __aeabi_fcmple
• __aeabi_fcmplt

are ported to Rust because compiler-rt doesn't provide an implementation of these for the thumbv6m-none-eabi target.

[hug-dev]

Should this now be closed?
#276 removed the thumbv6m config from the intrinsics example.

[AaronKutch]

This should be closed by now