Summary: Allow 0 compiler threads if no JIT is used.
Reviewed-by: kvn, dholmes
Contributed-by: NSeverin Gehwolf <sgehwolf@redhat.com>

Summary: Ensure appropriate min. number of compiler threads (1 for non-tiered, and 2 for tiered)
Reviewed-by: kvn

8028052: compiler/startup/SmallCodeCacheStartup.java fails there is no 'no space to run compiler' in the output
Summary: Weaken test so that configurations that have no C1 compiler pass
Reviewed-by: iveresov

8026949: -Xint flag prints wrong warning: Initialization of C1 thread failed (no space to run compilers)
Summary: Exit compiler threads early during startup so that wrong error message is not printed
Reviewed-by: iveresov, twisti

Summary: Ensure ensure correct initialization of compiler runtime
Reviewed-by: kvn, twisti