Auto merge of #75697 - lzutao:mir-dumb-const-prefix, r=oli-obk

Suppress "const" prefix of FnDef constants in MIR dump

I [was asked][1] to suppress the `const` infront of `FnDef`.
I tried to suppress comments for other types, but turned out that `const ()` and `()` is different: https://github.com/rust-lang/rust/pull/75697#discussion_r473892806

[1]: https://github.com/rust-lang/rust/pull/75670#issuecomment-675574333

src/test/ui/consts/const-extern-fn/const-extern-fn-call-extern-fn.stderr

@@ -1,4 +1,4 @@
-error[E0723]: can only call other `const fn` within a `const fn`, but `const regular_in_block` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `regular_in_block` is not stable as `const fn`
   --> $DIR/const-extern-fn-call-extern-fn.rs:9:9
    |
 LL |         regular_in_block();
@@ -7,7 +7,7 @@ LL |         regular_in_block();
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const regular` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `regular` is not stable as `const fn`
   --> $DIR/const-extern-fn-call-extern-fn.rs:18:9
    |
 LL |         regular();

src/test/ui/consts/min_const_fn/min_const_fn_libstd_stability.stderr

@@ -1,4 +1,4 @@
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo` is not stable as `const fn`
   --> $DIR/min_const_fn_libstd_stability.rs:16:25
    |
 LL | const fn bar() -> u32 { foo() }
@@ -7,7 +7,7 @@ LL | const fn bar() -> u32 { foo() }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2` is not stable as `const fn`
   --> $DIR/min_const_fn_libstd_stability.rs:24:26
    |
 LL | const fn bar2() -> u32 { foo2() }
@@ -25,7 +25,7 @@ LL | const fn bar3() -> u32 { (5f32 + 6f32) as u32 }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2_gated` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2_gated` is not stable as `const fn`
   --> $DIR/min_const_fn_libstd_stability.rs:38:32
    |
 LL | const fn bar2_gated() -> u32 { foo2_gated() }

src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability.stderr

@@ -1,4 +1,4 @@
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability.rs:16:41
    |
 LL | const unsafe fn bar() -> u32 { unsafe { foo() } }
@@ -7,7 +7,7 @@ LL | const unsafe fn bar() -> u32 { unsafe { foo() } }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability.rs:24:42
    |
 LL | const unsafe fn bar2() -> u32 { unsafe { foo2() } }
@@ -25,7 +25,7 @@ LL | const unsafe fn bar3() -> u32 { (5f32 + 6f32) as u32 }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2_gated` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2_gated` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability.rs:38:48
    |
 LL | const unsafe fn bar2_gated() -> u32 { unsafe { foo2_gated() } }

src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability2.stderr

@@ -1,4 +1,4 @@
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability2.rs:16:32
    |
 LL | const unsafe fn bar() -> u32 { foo() }
@@ -7,7 +7,7 @@ LL | const unsafe fn bar() -> u32 { foo() }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability2.rs:24:33
    |
 LL | const unsafe fn bar2() -> u32 { foo2() }
@@ -16,7 +16,7 @@ LL | const unsafe fn bar2() -> u32 { foo2() }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const foo2_gated` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `foo2_gated` is not stable as `const fn`
   --> $DIR/min_const_unsafe_fn_libstd_stability2.rs:33:39
    |
 LL | const unsafe fn bar2_gated() -> u32 { foo2_gated() }

src/test/ui/rfc-2632-const-trait-impl/const-check-fns-in-const-impl.stderr

@@ -1,4 +1,4 @@
-error[E0723]: can only call other `const fn` within a `const fn`, but `const non_const` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `non_const` is not stable as `const fn`
   --> $DIR/const-check-fns-in-const-impl.rs:12:16
    |
 LL |     fn foo() { non_const() }

src/test/ui/rfc-2632-const-trait-impl/stability.stderr

@@ -10,7 +10,7 @@ LL | |     }
    = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
    = help: add `#![feature(const_fn)]` to the crate attributes to enable
 
-error[E0723]: can only call other `const fn` within a `const fn`, but `const <Int as std::ops::Add>::add` is not stable as `const fn`
+error[E0723]: can only call other `const fn` within a `const fn`, but `<Int as std::ops::Add>::add` is not stable as `const fn`
   --> $DIR/stability.rs:32:5
    |
 LL |     Int(1i32) + Int(2i32)