internal/rosa: respect preferred job count

This discontinues use of nproc, and also overrides detection behaviour in ninja.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/perl.go

@@ -43,7 +43,7 @@ rm -f /system/bin/ps # perl does not like toybox ps
 			{"Duseshrplib"},
 		},
 		Check: []string{
-			"TEST_JOBS=256",
+			"TEST_JOBS=" + jobsLE,
 			"test_harness",
 		},
 		Install: `LD_LIBRARY_PATH="$PWD" ./perl -Ilib -I. installperl --destdir=/work`,