cmd/link: Add missing platform for Mac Catalyst

Fixes #67175

Defines a MachoPlatorm constant in OS_Darwin for MacCatalyst build. This enables adding the suffix $INODE64 on syscall methods needed for amd64 Darwin platform.

Change-Id: Ie677e241599e2a14359c5809fa9ddb3b63161629
GitHub-Last-Rev: feae982
GitHub-Pull-Request: #67176
Reviewed-on: https://go-review.googlesource.com/c/go/+/583295
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/link/internal/ld/macho.go

@@ -195,11 +195,12 @@ const (
 )
 
 const (
-	PLATFORM_MACOS    MachoPlatform = 1
-	PLATFORM_IOS      MachoPlatform = 2
-	PLATFORM_TVOS     MachoPlatform = 3
-	PLATFORM_WATCHOS  MachoPlatform = 4
-	PLATFORM_BRIDGEOS MachoPlatform = 5
+	PLATFORM_MACOS		MachoPlatform = 1
+	PLATFORM_IOS		MachoPlatform = 2
+	PLATFORM_TVOS		MachoPlatform = 3
+	PLATFORM_WATCHOS	MachoPlatform = 4
+	PLATFORM_BRIDGEOS	MachoPlatform = 5
+	PLATFORM_MACCATALYST	MachoPlatform = 6
 )
 
 // rebase table opcode
@@ -969,7 +970,7 @@ func collectmachosyms(ctxt *Link) {
 		// Some 64-bit functions have a "$INODE64" or "$INODE64$UNIX2003" suffix.
 		if t == sym.SDYNIMPORT && ldr.SymDynimplib(s) == "/usr/lib/libSystem.B.dylib" {
 			// But only on macOS.
-			if machoPlatform == PLATFORM_MACOS {
+			if machoPlatform == PLATFORM_MACOS || machoPlatform == PLATFORM_MACCATALYST {
 				switch n := ldr.SymExtname(s); n {
 				case "fdopendir":
 					switch buildcfg.GOARCH {