Auto merge of rust-lang#90791 - drmorr0:drmorr-memcmp-cint-cfg, r=petrochenkov

make memcmp return a value of c_int_width instead of i32

This is an attempt to fix rust-lang#32610 and rust-lang#78022, namely, that `memcmp` always returns an `i32` regardless of the platform.  I'm running into some issues and was hoping I could get some help.

Here's what I've been attempting so far:

1. Build the stage0 compiler with all the changes _expect_ for the changes in `library/core/src/slice/cmp.rs` and `compiler/rustc_codegen_llvm/src/context.rs`; this is because `target_c_int_width` isn't passed through and recognized as a valid config option yet.  I'm building with `./x.py build --stage 0 library/core library/proc_macro compiler/rustc`
2. Next I add in the `#[cfg(c_int_width = ...)]` params to `cmp.rs` and `context.rs` and build the stage 1 compiler by running `./x.py build --keep-stage 0 --stage 1 library/core library/proc_macro compiler/rustc`.  This step now runs successfully.
3. Lastly, I try to build the test program for AVR mentioned in rust-lang#78022 with `RUSTFLAGS="--emit llvm-ir" cargo build --release`, and look at the resulting llvm IR, which still shows:

```
...
%11 = call addrspace(1) i32 `@memcmp(i8*` nonnull %5, i8* nonnull %10, i16 5) #7, !dbg !1191                                                                                                                                                                                                                                %.not = icmp eq i32 %11, 0, !dbg !1191
...
; Function Attrs: nounwind optsize                                                                                                                                                                                                                                                                                          declare i32 `@memcmp(i8*,` i8*, i16) local_unnamed_addr addrspace(1) #4
```

Any ideas what I'm missing here?  Alternately, if this is totally the wrong approach I'm open to other suggestions.

cc `@Rahix`

Author: bors

core/src/ffi/mod.rs

@@ -57,6 +57,9 @@ type_alias! { "c_schar.md", c_schar = i8, NonZero_c_schar = NonZeroI8; }
 type_alias! { "c_uchar.md", c_uchar = u8, NonZero_c_uchar = NonZeroU8; }
 type_alias! { "c_short.md", c_short = i16, NonZero_c_short = NonZeroI16; }
 type_alias! { "c_ushort.md", c_ushort = u16, NonZero_c_ushort = NonZeroU16; }
+#[cfg(any(target_arch = "avr", target_arch = "msp430"))]
+type_alias! { "c_int.md", c_int = i16, NonZero_c_int = NonZeroI16; }
+#[cfg(not(any(target_arch = "avr", target_arch = "msp430")))]
 type_alias! { "c_int.md", c_int = i32, NonZero_c_int = NonZeroI32; }
 type_alias! { "c_uint.md", c_uint = u32, NonZero_c_uint = NonZeroU32; }
 type_alias! { "c_long.md", c_long = i32, NonZero_c_long = NonZeroI32;

core/src/slice/cmp.rs

@@ -1,6 +1,7 @@
 //! Comparison traits for `[T]`.
 
 use crate::cmp::{self, Ordering};
+use crate::ffi;
 use crate::mem;
 
 use super::from_raw_parts;
@@ -13,8 +14,7 @@ extern "C" {
     ///
     /// Returns 0 for equal, < 0 for less than and > 0 for greater
     /// than.
-    // FIXME(#32610): Return type should be c_int
-    fn memcmp(s1: *const u8, s2: *const u8, n: usize) -> i32;
+    fn memcmp(s1: *const u8, s2: *const u8, n: usize) -> ffi::c_int;
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]