Set SWIFTCI_USE_LOCAL_DEPS=1

Instructs auxiliary repos to use local clones rather than fresh checkouts
from Package.swift. This gives us more control over branches specified in
update-checkout-config.json. This resolves mismatches such as yams, which
currently points to a fork in one place, but not the other.

Author: texasmichelle

utils/build-toolchain-tensorflow

@@ -173,6 +173,9 @@ SWIFT_TOOLCHAIN_DIR="/Library/Developer/Toolchains/${TOOLCHAIN_NAME}.xctoolchain
 SYMBOLS_PACKAGE="${SRC_DIR}/${SYM_ARCHIVE}"
 DRY_RUN="${DRY_RUN}"
 
+# Instructs swift-driver, et al to use local clones.
+export SWIFTCI_USE_LOCAL_DEPS=1
+
 if [ ${INSTALLER_PACKAGE} ]; then
   INSTALLER_PACKAGE="darwin_toolchain_installer_package=${TOOLCHAIN_NAME}-osx.pkg"
 fi