bpo-38470: Fix test_compileall.test_compile_dir_maxlevels() (GH-16789)

bpo-38470: Fix test_compileall.test_compile_dir_maxlevels() (GH-16789)

Fix test_compile_dir_maxlevels() on Windows without long path
support: only create 3 subdirectories instead of between 20 and 100
subdirectories.

Fix also compile_dir() to use the current sys.getrecursionlimit()
value as the default maxlevels value, rather than using
sys.getrecursionlimit() value read at startup.