Refactor to use oldest_cpu

Library/Homebrew/extend/os/mac/hardware.rb

@@ -24,21 +24,4 @@ module Hardware
       generic_oldest_cpu
     end
   end
-
-  # Override
-  # Mirrors version-dependent logic of oldest_cpu
-  sig { params(version: T.nilable(Version)).returns(String) }
-  def self.rustflags_target_cpu(version = nil)
-    version = if version
-      MacOSVersion.new(version.to_s)
-    else
-      MacOS.version
-    end
-
-    if Hardware::CPU.intel? && version >= :mojave
-      "-Ctarget-cpu=nehalem"
-    else
-      generic_rustflags_target_cpu
-    end
-  end
 end

Library/Homebrew/hardware.rb

@@ -41,6 +41,14 @@ module Hardware
       end
       alias generic_optimization_flags optimization_flags
 
+      def rust_optimisation_flags
+        # Only give values where it is an improvement over rust cpu defaults
+        @rust_optimisation_flags ||= {
+          native:  "-Ctarget-cpu=native",
+          nehalem: "-Ctarget-cpu=nehalem",
+        }.freeze
+      end
+
       sig { returns(Symbol) }
       def arch_32_bit
         if arm?
@@ -221,11 +229,10 @@ module Hardware
     # But only where it is version dependent.
     # Rust already defaults to the oldest supported cpu for the target-triple
     # Including apple-m1 since 1.71.
-    sig { params(_version: T.nilable(Version)).returns(String) }
+    sig { returns(String) }
-    def rustflags_target_cpu(_version = nil)
+    def rustflags_target_cpu
-      ""
+      CPU.rust_optimisation_flags.fetch(oldest_cpu, "")
     end
-    alias generic_rustflags_target_cpu rustflags_target_cpu
   end
 end