Revert "swift: don't pass -march to swiftc"

This reverts commit 8a7841ceef.

pkgs/build-support/cc-wrapper/default.nix

@@ -53,10 +53,6 @@
 , gccForLibs ? if useCcForLibs then cc else null
 , fortify-headers ? null
 , includeFortifyHeaders ? null
-
-# https://github.com/NixOS/nixpkgs/issues/295322
-# should -march flag be used
-, disableMarch ? false
 }:
 
 assert nativeTools -> !propagateDoc && nativePrefix != "";
@@ -633,7 +629,7 @@ stdenv.mkDerivation {
 
     # TODO: aarch64-darwin has mcpu incompatible with gcc
     + optionalString ((targetPlatform ? gcc.arch) && !isClang && !(stdenv.isDarwin && stdenv.isAarch64) &&
-                      isGccArchSupported targetPlatform.gcc.arch && !disableMarch) ''
+                      isGccArchSupported targetPlatform.gcc.arch) ''
       echo "-march=${targetPlatform.gcc.arch}" >> $out/nix-support/cc-cflags-before
     ''
 
@@ -729,7 +725,7 @@ stdenv.mkDerivation {
     + optionalString isClang ''
       # Escape twice: once for this script, once for the one it gets substituted into.
       export march=${escapeShellArg
-        (optionalString (targetPlatform ? gcc.arch && !disableMarch)
+        (optionalString (targetPlatform ? gcc.arch)
           (escapeShellArg "-march=${targetPlatform.gcc.arch}"))}
       export defaultTarget=${targetPlatform.config}
       substituteAll ${./add-clang-cc-cflags-before.sh} $out/nix-support/add-local-cc-cflags-before.sh

pkgs/development/compilers/swift/default.nix

@@ -25,13 +25,9 @@ let
     #
     # The following selects the correct Clang version, matching the version
     # used in Swift, and applies the same libc overrides as `apple_sdk.stdenv`.
-    clang = let
-      # https://github.com/NixOS/nixpkgs/issues/295322
-      clangNoMarch = swiftLlvmPackages.clang.override { disableMarch = true; };
-    in
-    if pkgs.stdenv.isDarwin
+    clang = if pkgs.stdenv.isDarwin
       then
-        clangNoMarch.override rec {
+        swiftLlvmPackages.clang.override rec {
           libc = apple_sdk.Libsystem;
           bintools = pkgs.bintools.override { inherit libc; };
           # Ensure that Swift’s internal clang uses the same libc++ and libc++abi as the
@@ -41,7 +37,7 @@ let
           inherit (llvmPackages) libcxx;
         }
       else
-        clangNoMarch;
+        swiftLlvmPackages.clang;
 
     # Overrides that create a useful environment for swift packages, allowing
     # packaging with `swiftPackages.callPackage`. These are similar to