Fix macos broken build due to cmake 4.0 upgrade

Cmake version 4 changes the behaviour of the CMAKE_OSX_SYSROOT variable
so that it doesn't always get set. The build scripts use that variable
to determine which version of the SDK is installed, and will fail if the
variable is unset. The scripts need a different method to read the SDK
version.

'xcrun' is a more reliable way of getting the SDK version. The
--show-sdk-version flag returns the version number itself, and
--show-sdk-path gives a path that was previously in the
CMAKE_OSX_SYSROOT variable. Change the build scripts to use xcrun to
obtain the path.

Signed-off-by: Grant Likely <[email protected]>

Author: glikely

.github/scripts/build-macos

@@ -36,6 +36,9 @@ TRAPZERR() {
   exit 2
 }
 
+# Hack to work around cmake4 behaviour change on CMAKE_OSX_SYSROOT
+export SYSROOT=$(xcrun --sdk macosx --show-sdk-path)
+
 build() {
   if (( ! ${+SCRIPT_HOME} )) typeset -g SCRIPT_HOME=${ZSH_ARGZERO:A:h}
   local host_os='macos'

cmake/macos/compilerconfig.cmake

@@ -17,9 +17,11 @@ add_compile_options("$<$<NOT:$<COMPILE_LANGUAGE:Swift>>:-fopenmp-simd>")
 # Ensure recent enough Xcode and platform SDK
 set(_obs_macos_minimum_sdk 15.0) # Keep in sync with Xcode
 set(_obs_macos_minimum_xcode 16.0) # Keep in sync with SDK
-message(DEBUG "macOS SDK Path: ${CMAKE_OSX_SYSROOT}")
-string(REGEX MATCH ".+/MacOSX.platform/Developer/SDKs/MacOSX([0-9]+\\.[0-9])+\\.sdk$" _ ${CMAKE_OSX_SYSROOT})
-set(_obs_macos_current_sdk ${CMAKE_MATCH_1})
+execute_process(
+  COMMAND xcrun --sdk macosx --show-sdk-version
+  OUTPUT_VARIABLE _obs_macos_current_sdk
+  WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+  OUTPUT_STRIP_TRAILING_WHITESPACE)
 message(DEBUG "macOS SDK version: ${_obs_macos_current_sdk}")
 if(_obs_macos_current_sdk VERSION_LESS _obs_macos_minimum_sdk)
   message(