rcs-5.9.4: make check: 8 of 51 tests failed on AIX

After adding
export LDFLAGS='-lpthread'; ./configure ...; make;
make check
returns
...
make[2]: Entering directory `/data/prj/gnu/rcs/rcs-5.9.4/tests'
PASS: t010
PASS: t030
PASS: t050
PASS: t150
PASS: t153
PASS: t160
PASS: t180
PASS: t300
PASS: t301
PASS: t310
PASS: t311
PASS: t312
PASS: t313
PASS: t320
PASS: t370
PASS: t380
PASS: t390
PASS: t391
PASS: t400
PASS: t410
PASS: t420
PASS: t430
PASS: t440
PASS: t450
PASS: t460
PASS: t470
FAIL: t510
FAIL: t511
PASS: t600
PASS: t601
PASS: t602
FAIL: t603
FAIL: t604
FAIL: t605
PASS: t606
PASS: t607
PASS: t608
PASS: t609
PASS: t620
PASS: t630
PASS: t780
PASS: t790
PASS: t800
PASS: t801
PASS: t802
PASS: t803
FAIL: t804
PASS: t805
PASS: t810
FAIL: t900
FAIL: t999
================================
8 of 51 tests failed
Please report to [email protected]
================================
make[2]: *** [check-TESTS] Error 1
make[2]: Leaving directory `/data/prj/gnu/rcs/rcs-5.9.4/tests'
make[1]: *** [check-am] Error 2
make[1]: Leaving directory `/data/prj/gnu/rcs/rcs-5.9.4/tests'
make: *** [check-recursive] Error 1
root@x064:[/data/prj/gnu/rcs/rcs-5.9.4]