[6.0] CMake: amend search path for Swift content from Darwin toolchain

Additional testing showed that the path I initially choose does not work
in all scenarios.

Expands on #73255
Still addresses rdar://127014753

(cherry picked from commit 291065d)

Author: edymtt

cmake/modules/AddSwift.cmake

@@ -612,7 +612,7 @@ function(_add_swift_runtime_link_flags target relpath_to_lib_dir bootstrapping)
       endif()
     endif()
     if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS AND SWIFT_ALLOW_LINKING_SWIFT_CONTENT_IN_DARWIN_TOOLCHAIN)
-      get_filename_component(TOOLCHAIN_BIN_DIR ${SWIFT_EXEC_FOR_SWIFT_MODULES} DIRECTORY)
+      get_filename_component(TOOLCHAIN_BIN_DIR ${CMAKE_Swift_COMPILER} DIRECTORY)
       get_filename_component(TOOLCHAIN_LIB_DIR "${TOOLCHAIN_BIN_DIR}/../lib/swift/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}" ABSOLUTE)
       target_link_directories(${target} BEFORE PUBLIC ${TOOLCHAIN_LIB_DIR})
     endif()

tools/SourceKit/cmake/modules/AddSwiftSourceKit.cmake

@@ -175,7 +175,7 @@ function(add_sourcekit_swift_runtime_link_flags target path HAS_SWIFT_MODULES)
     endif()
 
     if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS AND SWIFT_ALLOW_LINKING_SWIFT_CONTENT_IN_DARWIN_TOOLCHAIN)
-      get_filename_component(TOOLCHAIN_BIN_DIR ${SWIFT_EXEC_FOR_SWIFT_MODULES} DIRECTORY)
+      get_filename_component(TOOLCHAIN_BIN_DIR ${CMAKE_Swift_COMPILER} DIRECTORY)
       get_filename_component(TOOLCHAIN_LIB_DIR "${TOOLCHAIN_BIN_DIR}/../lib/swift/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}" ABSOLUTE)
       target_link_directories(${target} BEFORE PUBLIC ${TOOLCHAIN_LIB_DIR})
     endif()