[AVR][NO UPSTREAM] Disable the floating point conversion and bignum m…

…odules

These do not compile because of avr-rust/rust-legacy-fork#92.

The error message looks like

```
Impossible reg-to-reg copy
UNREACHABLE executed at /home/dylan/projects/llvm-project/llvm/lib/Target/AVR/AVRInstrInfo.cpp:75!
Stack dump:
0.	Program arguments: ./bin/llc -march=avr -mcpu=atmega328p bugpoint-reduced-simplified.ll -o /dev/null
1.	Running pass 'Function Pass Manager' on module 'bugpoint-reduced-simplified.ll'.
2. Running pass 'Post-RA pseudo instruction expansion pass' on function '@_ZN3lib3num7flt2dec8strategy5grisu22max_pow10_no_more_than17h83b3c65a945b5158E'
```

avr-rust/rust-legacy-fork#92

core/fmt/float.rs

@@ -10,11 +10,13 @@
 
 use fmt::{Formatter, Result, LowerExp, UpperExp, Display, Debug};
 use mem;
+#[cfg(not(target_arch = "avr"))]
 use num::flt2dec;
 
 // Don't inline this so callers don't use the stack space this function
 // requires unless they have to.
 #[inline(never)]
+#[cfg(not(target_arch = "avr"))]
 fn float_to_decimal_common_exact<T>(fmt: &mut Formatter, num: &T,
                                     sign: flt2dec::Sign, precision: usize) -> Result
     where T: flt2dec::DecodableFloat

core/fmt/mod.rs

@@ -15,12 +15,14 @@
 use cell::{UnsafeCell, Cell, RefCell, Ref, RefMut};
 use marker::PhantomData;
 use mem;
+#[cfg(not(target_arch = "avr"))]
 use num::flt2dec;
 use ops::Deref;
 use result;
 use slice;
 use str;
 
+#[cfg(not(target_arch = "avr"))]
 mod float;
 mod num;
 mod builders;
@@ -1262,6 +1264,7 @@ impl<'a> Formatter<'a> {
     /// Takes the formatted parts and applies the padding.
     /// Assumes that the caller already has rendered the parts with required precision,
     /// so that `self.precision` can be ignored.
+    #[cfg(not(target_arch = "avr"))]
     fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
         if let Some(mut width) = self.width {
             // for the sign-aware zero padding, we render the sign first and
@@ -1301,6 +1304,7 @@ impl<'a> Formatter<'a> {
         }
     }
 
+    #[cfg(not(target_arch = "avr"))]
     fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
         fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
             buf.write_str(unsafe { str::from_utf8_unchecked(s) })

core/num/mod.rs

@@ -91,8 +91,11 @@ impl<T: fmt::UpperHex> fmt::UpperHex for Wrapping<T> {
 mod wrapping;
 
 // All these modules are technically private and only exposed for coretests:
+#[cfg(not(target_arch = "avr"))]
 pub mod flt2dec;
+#[cfg(not(target_arch = "avr"))]
 pub mod dec2flt;
+#[cfg(not(target_arch = "avr"))]
 pub mod bignum;
 pub mod diy_float;
 
@@ -3577,6 +3580,7 @@ impl fmt::Display for ParseIntError {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(not(target_arch = "avr"))]
 pub use num::dec2flt::ParseFloatError;
 
 // Conversion traits for primitive integer and float types