[CMake] Make sure ICU libdir is correctly added to library_search_directories

The CMake variables ${sdk} and ${arch} are only set if
_add_variant_link_flags is invoked from add_swift_target_library calling
_add_swift_library_single. If you get to _add_swift_library_single from
add_swift_host_library, those variables will not be set and subsequent
linking will not find ICU libraries. This was an issue when building
swift host libraries on Android.

Author: bulbazord

cmake/modules/AddSwift.cmake

@@ -467,12 +467,14 @@ function(_add_variant_link_flags)
   endif()
 
   if(NOT "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_UC}" STREQUAL "")
-    get_filename_component(SWIFT_${sdk}_${arch}_ICU_UC_LIBDIR "${SWIFT_${sdk}_${arch}_ICU_UC}" DIRECTORY)
-    list(APPEND library_search_directories "${SWIFT_${sdk}_${arch}_ICU_UC_LIBDIR}")
+    get_filename_component(SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_UC_LIBDIR
+      "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_UC}" DIRECTORY)
+    list(APPEND library_search_directories "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_UC_LIBDIR}")
   endif()
   if(NOT "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_I18N}" STREQUAL "")
-    get_filename_component(SWIFT_${sdk}_${arch}_ICU_I18N_LIBDIR "${SWIFT_${sdk}_${arch}_ICU_I18N}" DIRECTORY)
-    list(APPEND library_search_directories "${SWIFT_${sdk}_${arch}_ICU_I18N_LIBDIR}")
+    get_filename_component(SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_I18N_LIBDIR
+      "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_I18N}" DIRECTORY)
+    list(APPEND library_search_directories "${SWIFT_${LFLAGS_SDK}_${LFLAGS_ARCH}_ICU_I18N_LIBDIR}")
   endif()
 
   if(NOT SWIFT_COMPILER_IS_MSVC_LIKE)