Incorporate review feedback from Micheal

Author: edymtt

cmake/modules/AddSwift.cmake

@@ -1261,9 +1261,11 @@ 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}")
 
-  # There are scenarios in which this function is called with SDKROOT set
-  # In those we need to ensure we link against the dylibs present in the SDK
-  if(DEFINED ENV{SDKROOT})
+  # 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()