Pass SwiftSyntax path to scl-f build

Author: jmschonfeld

utils/build-script-impl

@@ -2522,6 +2522,8 @@ for host in "${ALL_HOSTS[@]}"; do
                   -DFOUNDATION_PATH_TO_LIBDISPATCH_BUILD=$(build_directory ${host} libdispatch)
                   -Ddispatch_DIR=$(build_directory ${host} libdispatch)/cmake/modules
 
+                  -DSwiftSyntax_DIR=$(build_directory ${host} swift)/cmake/modules
+
                   -D_SwiftFoundation_SourceDIR=${FOUNDATION_SWIFTFOUNDATION_SOURCE_DIR}
                   -D_SwiftFoundationICU_SourceDIR=${FOUNDATION_SWIFTFOUNDATIONICU_SOURCE_DIR}
                   -D_SwiftCollections_SourceDIR=${SWIFT_COLLECTIONS_SOURCE_DIR}