[build-script] Tie llvm, swift, and lldb to the same sysroot

rdar://62895058

Author: vedantk

utils/build-script-impl

@@ -705,6 +705,10 @@ function set_build_options_for_host() {
                 # in the compiler checks CMake performs
                 -DCMAKE_OSX_ARCHITECTURES="${architecture}"
             )
+
+            lldb_cmake_options+=(
+                -DCMAKE_OSX_SYSROOT:PATH="${cmake_os_sysroot}"
+            )
             ;;
     esac