[executorch] Update iOS toolchain with a modern cmake syntax. (pytorch#115799)

Summary: Replace exec_program with execute_process

Test Plan: CI

Differential Revision: D52147108

Pull Request resolved: pytorch#115799
Approved by: https://github.com/huydhn

Author: shoumikhin

cmake/iOS.cmake

@@ -41,7 +41,7 @@ set(CMAKE_OSX_DEPLOYMENT_TARGET "" CACHE STRING "Force unset of the deployment t
 # Determine the cmake host system version so we know where to find the iOS SDKs
 find_program(CMAKE_UNAME uname /bin /usr/bin /usr/local/bin)
 if(CMAKE_UNAME)
-    exec_program(uname ARGS -r OUTPUT_VARIABLE CMAKE_HOST_SYSTEM_VERSION)
+    execute_process(COMMAND uname -r OUTPUT_VARIABLE CMAKE_HOST_SYSTEM_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)
     string(REGEX REPLACE "^([0-9]+)\\.([0-9]+).*$" "\\1" DARWIN_MAJOR_VERSION "${CMAKE_HOST_SYSTEM_VERSION}")
 endif(CMAKE_UNAME)
 
@@ -127,7 +127,11 @@ set(IOS_DEPLOYMENT_TARGET ${IOS_DEPLOYMENT_TARGET} CACHE STRING "Minimum iOS ver
 
 # Setup iOS developer location unless specified manually with CMAKE_IOS_DEVELOPER_ROOT
 # Note Xcode 4.3 changed the installation location, choose the most recent one available
-exec_program(/usr/bin/xcode-select ARGS -print-path OUTPUT_VARIABLE CMAKE_XCODE_DEVELOPER_DIR)
+execute_process(
+    COMMAND /usr/bin/xcode-select -print-path
+    OUTPUT_VARIABLE CMAKE_XCODE_DEVELOPER_DIR
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+)
 set(XCODE_POST_43_ROOT "${CMAKE_XCODE_DEVELOPER_DIR}/Platforms/${IOS_PLATFORM_LOCATION}/Developer")
 set(XCODE_PRE_43_ROOT "/Developer/Platforms/${IOS_PLATFORM_LOCATION}/Developer")
 if(NOT CMAKE_IOS_DEVELOPER_ROOT)