[compiler-rt] Use xcrun instead of xcodebuild to find the SDK directory

[arichardson]

Summary

xcodebuild does not work unless XCode is installed whereas xcrun also work
when only the Command Line Tools are installed. Unlike the check for the
version (D69610), this did not cause an erro for me since the fallback to
/usr/include for the OSX sysroot worked.

[yln]

Thanks Alexander! I did not run this on my machine, but since D69610 worked I think this should too.

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

function(find_darwin_sdk_dir var sdk_name)
 
   if(DARWIN_${sdk_name}_CACHED_SYSROOT)
     set(${var} ${DARWIN_${sdk_name}_CACHED_SYSROOT} PARENT_SCOPE)
     return()
   endif()
   if(NOT DARWIN_PREFER_PUBLIC_SDK)
     # Let's first try the internal SDK, otherwise use the public SDK.
     execute_process(
-      COMMAND xcodebuild -version -sdk ${sdk_name}.internal Path
+      COMMAND xcrun --sdk ${sdk_name}.internal --show-sdk-path
       RESULT_VARIABLE result_process
       OUTPUT_VARIABLE var_internal
       OUTPUT_STRIP_TRAILING_WHITESPACE
       ERROR_FILE /dev/null
     )
   endif()
   if((NOT result_process EQUAL 0) OR "" STREQUAL "${var_internal}")
     execute_process(
-      COMMAND xcodebuild -version -sdk ${sdk_name} Path
+      COMMAND xcrun --sdk ${sdk_name} --show-sdk-path
       RESULT_VARIABLE result_process
       OUTPUT_VARIABLE var_internal
       OUTPUT_STRIP_TRAILING_WHITESPACE
       ERROR_FILE /dev/null
     )
   else()
     set(${var}_INTERNAL ${var_internal} PARENT_SCOPE)
   endif()
   if(result_process EQUAL 0)
     set(${var} ${var_internal} PARENT_SCOPE)
   endif()
+  message(STATUS "Checking DARWIN_${sdk_name}_SYSROOT - '${var_internal}'")
   set(DARWIN_${sdk_name}_CACHED_SYSROOT ${var_internal} CACHE STRING "Darwin SDK path for SDK ${sdk_name}." FORCE)
 endfunction()
 
 function(find_darwin_sdk_version var sdk_name)
   # We deliberately don't cache the result here because
   # CMake's caching causes too many problems.
   set(result_process 1)
   if(NOT DARWIN_PREFER_PUBLIC_SDK)

compiler-rt/cmake/config-ix.cmake

if(APPLE)
   find_darwin_sdk_dir(DARWIN_iossim_SYSROOT iphonesimulator)
   find_darwin_sdk_dir(DARWIN_ios_SYSROOT iphoneos)
   find_darwin_sdk_dir(DARWIN_watchossim_SYSROOT watchsimulator)
   find_darwin_sdk_dir(DARWIN_watchos_SYSROOT watchos)
   find_darwin_sdk_dir(DARWIN_tvossim_SYSROOT appletvsimulator)
   find_darwin_sdk_dir(DARWIN_tvos_SYSROOT appletvos)
 
   if(NOT DARWIN_osx_SYSROOT)
+    message(WARNING "Could not determine OS X sysroot, trying /usr/include")
     if(EXISTS /usr/include)
       set(DARWIN_osx_SYSROOT /)
     else()
       message(ERROR "Could not detect OS X Sysroot. Either install Xcode or the Apple Command Line Tools")
     endif()
   endif()
 
   if(COMPILER_RT_ENABLE_IOS)