macho: handle -arch_multiple flag

flake.nix

@@ -65,7 +65,8 @@
           '';
         };
 
-        devShells.default = pkgs.mkShell {
+        devShells.default = pkgs.stdenvNoCC.mkDerivation {
+          name = "emerald";
           buildInputs = commonInputs ++ (with pkgs; [
             zlspkgs.default
             tracy

src/MachO.zig

@@ -1334,7 +1334,19 @@ fn reportUndefs(self: *MachO) !void {
 
         const err = try addFn(&self.base, nnotes);
         defer err.unlock();
-        try err.addMsg("undefined symbol: {s}", .{undef_sym.getName(self)});
+
+        if (self.options.arch_multiple) {
+            // When clang is invoked with two -arch flags, it will pass -arch_multiple and -final_output to the linker.
+            // According to LLD implementation [1], -arch_multiple is only used to signal to the linker that it should
+            // suffix undefined symbols errors/warnings with current architecture.
+            // [1]: https://reviews.llvm.org/D105450
+            try err.addMsg("undefined symbol for architecture {s}: {s}", .{
+                @tagName(self.options.cpu_arch.?),
+                undef_sym.getName(self),
+            });
+        } else {
+            try err.addMsg("undefined symbol: {s}", .{undef_sym.getName(self)});
+        }
 
         switch (notes) {
             .force_undefined => try err.addNote("referenced with linker flag -u", .{}),

src/MachO/Options.zig

@@ -25,6 +25,8 @@ const usage =
     \\-no_adhoc_codesign                 Does not generate adhoc code signature
     \\-all_load                          Loads all members of all static archive libraries
     \\-arch [name]                       Specifies which architecture the output file should be
+    \\-arch_multiple                     Specifies that the linker should augment error and warning
+    \\                                   messages with the architecture name.
     \\-current_version [value]           Specifies the current version number of the library
     \\-compatibility_version [value]     Specifies the compatibility version number of the library
     \\-dead_strip                        Remove functions and data that are unreachable by the entry point or 
@@ -105,6 +107,7 @@ dylib: bool = false,
 relocatable: bool = false,
 dynamic: bool = false,
 cpu_arch: ?std.Target.Cpu.Arch = null,
+arch_multiple: bool = false,
 platform: ?Platform = null,
 sdk_version: ?Version = null,
 inferred_platform_versions: [supported_platforms.len]Platform = undefined,
@@ -282,6 +285,8 @@ pub fn parse(arena: Allocator, args: []const []const u8, ctx: anytype) !Options
             } else {
                 ctx.fatal("Could not parse CPU architecture from '{s}'\n", .{value});
             }
+        } else if (p.flag1("arch_multiple")) {
+            opts.arch_multiple = true;
         } else if (p.arg1("macos_version_min")) |ver| {
             const min_ver = Version.parse(ver) orelse
                 ctx.fatal("Unable to parse version from '{s}'\n", .{version});