Do not run different compiler versions in the same directory due to possible cache conflicts when you specify -instance=extern. Consider the following when you compile with the -instances=extern template model:
Do not create unrelated binaries in the same directory. Any binaries (.o, .a, .so, executable programs) created in the same directory should be related, in that names of all objects, functions, and types common to two or more object files have identical definitions.
It is safe to run multiple compilations simultaneously in the same directory, such as when using dmake. It is not safe to run any compilations or link steps at the same time as another link step. A link step is any operation that creates a library or executable program. Be sure that dependencies in a makefile do not allow any commands to run in parallel with a link step.