When doing a rebuild of any target (slowdebug, release tested) after any changes in the hotspot sources, that rebuild fails with

Building target 'default (exploded-image)' in configuration 'linux-x86_64-normal-server-slowdebug'
Building JVM variant 'server' with features 'all-gcs cds closed-src commercial-features compiler1 compiler2 fprof jni-check jvmci jvmti management nmt services trace vm-structs'
Updating libjvm.so due to 1 file(s)
...hs/build/linux-x86_64-normal-server-slowdebug/hotspot/variant-server/libjvm/gtest/launcher-objs/gtestLauncher.o: In function `main':
...hs/hotspot/test/native/gtestLauncher.cpp:32: undefined reference to `runUnitTests'
collect2: error: ld returned 1 exit status
gmake[4]: *** [...hs/build/linux-x86_64-normal-server-slowdebug/hotspot/variant-server/libjvm/gtest/gtestLauncher] Error 1
gmake[4]: *** Waiting for unfinished jobs....
gmake[3]: *** [variant-server-libs] Error 2
gmake[2]: *** [hotspot] Error 1

The only way for a succeeding build seems to be cleaning out all artifacts first.

Ie.

bash configure ...
make CONF=<whatever> succeeds

any rebuild using

make CONF=<whatever>

fails.