macOS 27 build fixes + transition to UTType for file pickers (#5937)

* Get the viewer building on macOS 27

* Strip -mmacosx-version-min when we're below an SDK supported version.

Substitutes an actual SDK supported minimum version.

* Move kIOMainPortDefault behind an SDK compatibility check.

* Update llwindowmacosx_iokit.h

* Update llwindowmacosx_iokit.h

3 files changed, 38 insertions, 2 deletions

diff --git a/indra/llwindow/CMakeLists.txt b/indra/llwindow/CMakeLists.txt
index 13a7592e8f..3dae2d1067 100644
--- a/indra/llwindow/CMakeLists.txt
+++ b/indra/llwindow/CMakeLists.txt
@@ -60,6 +60,7 @@ set(macosx_HEADER_FILES
     llkeyboardmacosx.h
     llwindowmacosx.h
     llwindowmacosx-objc.h
+    llwindowmacosx_iokit.h
     llopenglview-objc.h
     llappdelegate-objc.h
     )
diff --git a/indra/llwindow/llwindowmacosx.cpp b/indra/llwindow/llwindowmacosx.cpp
index f8920318d3..1dd795cd3a 100644
--- a/indra/llwindow/llwindowmacosx.cpp
+++ b/indra/llwindow/llwindowmacosx.cpp
@@ -44,7 +44,7 @@
 #include <CoreGraphics/CGDisplayConfiguration.h>
 
 #include <IOKit/IOCFPlugIn.h>
-#include <IOKit/IOKitLib.h>
+#include "llwindowmacosx_iokit.h"
 #include <IOKit/IOMessage.h>
 #include <IOKit/hid/IOHIDUsageTables.h>
 #include <IOKit/hid/IOHIDLib.h>
@@ -2379,7 +2379,7 @@ bool LLWindowMacOSX::getInputDevices(U32 device_type_filter,
     io_iterator_t io_iter = 0;
 
     // create an IO object iterator
-    result = IOServiceGetMatchingServices( kIOMasterPortDefault, device_dict_ref, &io_iter );
+    result = IOServiceGetMatchingServices( kLLIOMainPort, device_dict_ref, &io_iter );
     if ( kIOReturnSuccess != result )
     {
         LL_WARNS("Joystick") << "IOServiceGetMatchingServices failed" << LL_ENDL;
diff --git a/indra/llwindow/llwindowmacosx_iokit.h b/indra/llwindow/llwindowmacosx_iokit.h
new file mode 100644
index 0000000000..a6be2c86ef
--- /dev/null
+++ b/indra/llwindow/llwindowmacosx_iokit.h
@@ -0,0 +1,35 @@
+/**
+ * @file llwindowmacosx_iokit.h
+ * @brief IOKit compatibility for macOS deployment target differences
+ *
+ * $LicenseInfo:firstyear=2025&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2025, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#pragma once
+#include <IOKit/IOKitLib.h>
+
+// kIOMainPortDefault is the macOS 12+ rename of kIOMasterPortDefault.
+#if __MAC_OS_X_VERSION_MIN_REQUIRED >= 120000
+static const mach_port_t kLLIOMainPort = kIOMainPortDefault;
+#else
+static const mach_port_t kLLIOMainPort = kIOMasterPortDefault;
+#endif