results/ is used as a clean target instead of test/results/

[jnasbyupgrade]

Fix seems as simple as

EXTRA_CLEAN -= results/
EXTRA_CLEAN += $(TESTDIR)/results/

[jnasbyupgrade]

Note: -= is not valid GNU Make syntax. Make 3.81 silently tolerates it, but Make 4.4+ correctly rejects it with a parse error.

The fix should use filter-out instead:

EXTRA_CLEAN := $(filter-out results/,$(EXTRA_CLEAN))
EXTRA_CLEAN += $(TESTOUT)/results/

(TESTOUT rather than TESTDIR in case they differ — TESTOUT is where --outputdir points.)