adjust_abi: make fallback logic for x86 ABIs a bit easier to read

Author: RalfJung

compiler/rustc_target/src/spec/mod.rs

@@ -2871,11 +2871,16 @@ impl Target {
             EfiApi => C { unwind: false },
 
             // See commentary in `is_abi_supported`.
-            Stdcall { .. } | Thiscall { .. } if self.arch == "x86" => abi,
-            Stdcall { unwind } | Thiscall { unwind } => C { unwind },
-            Fastcall { .. } if self.arch == "x86" => abi,
-            Vectorcall { .. } if ["x86", "x86_64"].contains(&&self.arch[..]) => abi,
-            Fastcall { unwind } | Vectorcall { unwind } => C { unwind },
+            Stdcall { unwind } | Thiscall { unwind } | Fastcall { unwind } => {
+                if self.arch == "x86" { abi } else { C { unwind } }
+            }
+            Vectorcall { unwind } => {
+                if ["x86", "x86_64"].contains(&&*self.arch) {
+                    abi
+                } else {
+                    C { unwind }
+                }
+            }
 
             // The Windows x64 calling convention we use for `extern "Rust"`
             // <https://learn.microsoft.com/en-us/cpp/build/x64-software-conventions#register-volatility-and-preservation>