Clean the derived data between builds to help reduce flakiness (#3150)

 Trying to fix #3146

Author: Corrob

scripts/build.sh

@@ -179,6 +179,9 @@ if [[ -n "${SANITIZERS:-}" ]]; then
   done
 fi
 
+# Clean the Derived Data between builds to help reduce flakiness.
+rm -rf ~/Library/Developer/Xcode/DerivedData
+
 case "$product-$method-$platform" in
   Firebase-xcodebuild-*)
     RunXcodebuild \