Merge pull request swiftlang#28127 from edymtt/search-in-sdkroot

Build: search libraries in Apple SDKs (if needed)

Author: edymtt

cmake/modules/AddSwift.cmake

@@ -1261,6 +1261,14 @@ function(_add_swift_library_single target name)
       "${SWIFT_NATIVE_SWIFT_TOOLS_PATH}/../lib/swift/${SWIFTLIB_SINGLE_SUBDIR}"
       "${SWIFT_NATIVE_SWIFT_TOOLS_PATH}/../lib/swift/${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_LIB_SUBDIR}")
 
+  # In certain cases when building, the environment variable SDKROOT is set to override
+  # where the sdk root is located in the system. If that environment variable has been
+  # set by the user, respect it and add the specified SDKROOT directory to the
+  # library_search_directories so we are able to link against those libraries
+  if(DEFINED ENV{SDKROOT} AND EXISTS "$ENV{SDKROOT}/usr/lib/swift")
+      list(APPEND library_search_directories "$ENV{SDKROOT}/usr/lib/swift")
+  endif()
+
   # Add variant-specific flags.
   if(SWIFTLIB_SINGLE_TARGET_LIBRARY)
     set(build_type "${SWIFT_STDLIB_BUILD_TYPE}")