"make -j10 test" incorrectly fails all tests

[Stefan Becker]

Test case:

$ make clean
...
$ git clean -xfd
...
# See issue #59 why we need to build "kati" first
$ make -j10 kati
...
$ GOPATH=/usr/share/gocode make -j10 test
g++ -c -std=c++11 -g -W -Wall -MMD -MP -O -DNOLOG -march=native -o affinity.o affinity.cc
g++ -c -std=c++11 -g -W -Wall -MMD -MP -O -DNOLOG -march=native -o command.o command.cc
...
multi_explicit_output_patterns.mk: FAIL
--- out.make    2016-04-27 10:50:45.200593757 +0300
+++ out.kati    2016-04-27 10:50:45.200593757 +0300
@@ -1,5 +1,4 @@
 === test ===
-warning: jobserver unavailable: using -j1.  Add "+" to parent make rule.
 echo azz
 azz
 echo zza
multi_explicit_output_patterns_double_colon.mk: FAIL (expected)
multi_implicit_output_patterns.mk has a string "FAIL" in its expectation
Makefile:21: recipe for target 'test' failed
make: *** [test] Error 1