Rollup merge of #141569 - workingjubilee:canonicalize-abi, r=bjorn3

Replace ad-hoc ABI "adjustments" with an `AbiMap` to `CanonAbi`

Our `conv_from_spec_abi`, `adjust_abi`, and `is_abi_supported` combine to give us a very confusing way of reasoning about what _actual_ calling convention we want to lower our code to and whether we want to compile the resulting code at all. Instead of leaving this code as a miniature adventure game in which someone tries to combine stateful mutations into a Rube Goldberg machine that will let them escape the maze and arrive at the promised land of codegen, we let `AbiMap` devour this complexity. Once you have an `AbiMap`, you can answer which `ExternAbi`s will lower to what `CanonAbi`s (and whether they will lower at all).

Removed:
- `conv_from_spec_abi` replaced by `AbiMap::canonize_abi`
- `adjust_abi` replaced by same
- `Conv::PreserveAll` as unused
- `Conv::Cold` as unused
- `enum Conv` replaced by `enum CanonAbi`

target-spec.json changes:
- If you have a target-spec.json then now your "entry-abi" key will be specified in terms of one of the `"{abi}"` strings Rust recognizes, e.g.
```json
    "entry-abi": "C",
    "entry-abi": "win64",
    "entry-abi": "aapcs",
```

1 files changed, 6 insertions, 32 deletions

diff --git a/compiler/rustc_target/src/json.rs b/compiler/rustc_target/src/json.rs
index 8d6f8f4c6f6..4fcc477921b 100644
--- a/compiler/rustc_target/src/json.rs
+++ b/compiler/rustc_target/src/json.rs
@@ -92,38 +92,6 @@ impl<A: ToJson> ToJson for Option<A> {
     }
 }
 
-impl ToJson for crate::callconv::Conv {
-    fn to_json(&self) -> Json {
-        let buf: String;
-        let s = match self {
-            Self::C => "C",
-            Self::Rust => "Rust",
-            Self::Cold => "Cold",
-            Self::PreserveMost => "PreserveMost",
-            Self::PreserveAll => "PreserveAll",
-            Self::ArmAapcs => "ArmAapcs",
-            Self::CCmseNonSecureCall => "CCmseNonSecureCall",
-            Self::CCmseNonSecureEntry => "CCmseNonSecureEntry",
-            Self::Msp430Intr => "Msp430Intr",
-            Self::X86Fastcall => "X86Fastcall",
-            Self::X86Intr => "X86Intr",
-            Self::X86Stdcall => "X86Stdcall",
-            Self::X86ThisCall => "X86ThisCall",
-            Self::X86VectorCall => "X86VectorCall",
-            Self::X86_64SysV => "X86_64SysV",
-            Self::X86_64Win64 => "X86_64Win64",
-            Self::GpuKernel => "GpuKernel",
-            Self::AvrInterrupt => "AvrInterrupt",
-            Self::AvrNonBlockingInterrupt => "AvrNonBlockingInterrupt",
-            Self::RiscvInterrupt { kind } => {
-                buf = format!("RiscvInterrupt({})", kind.as_str());
-                &buf
-            }
-        };
-        Json::String(s.to_owned())
-    }
-}
-
 impl ToJson for TargetMetadata {
     fn to_json(&self) -> Json {
         json!({
@@ -140,3 +108,9 @@ impl ToJson for rustc_abi::Endian {
         self.as_str().to_json()
     }
 }
+
+impl ToJson for rustc_abi::CanonAbi {
+    fn to_json(&self) -> Json {
+        self.to_string().to_json()
+    }
+}