Fix problem preventing new build system from using custom toolchains (#19509)

Author: johnno1962

utils/build-toolchain

@@ -97,6 +97,7 @@ YEAR=$(date +"%Y")
 MONTH=$(date +"%m")
 DAY=$(date +"%d")
 TOOLCHAIN_VERSION="swift-LOCAL-${YEAR}-${MONTH}-${DAY}-a"
+DARWIN_TOOLCHAIN_VERSION="0.0.${YEAR}${MONTH}${DAY}"
 ARCHIVE="${TOOLCHAIN_VERSION}-osx.tar.gz"
 SYM_ARCHIVE="${TOOLCHAIN_VERSION}-osx-symbols.tar.gz"
 BUNDLE_PREFIX=${BUNDLE_PREFIX:?Please specify a bundle prefix}
@@ -123,5 +124,5 @@ DISTCC_FLAG="${DISTCC_FLAG}"
         darwin_toolchain_display_name="${DISPLAY_NAME}" \
         darwin_toolchain_display_name_short="${DISPLAY_NAME_SHORT}" \
         darwin_toolchain_xctoolchain_name="${TOOLCHAIN_NAME}" \
-        darwin_toolchain_version="${TOOLCHAIN_VERSION}" \
+        darwin_toolchain_version="${DARWIN_TOOLCHAIN_VERSION}" \
         darwin_toolchain_alias="Local"