When working on reproducible builds for openSUSE, I found that
building the ibutils package with -j1 or -j2
always fails:

openSUSE:Factory/ibutils # osc build --no-service -j1

Actual result:
[   54s] libtool: link: g++ -I/usr/include -I/usr/include/infiniband -I/usr/incl
ude -DOSM_VENDOR_INTF_OPENIB -DOSM_BUILD_OPENIB -D_XOPEN_SOURCE=600 -D_BSD_SOURC
E=1 -O2 -Wall -fno-strict-aliasing -fPIC -DIBIS_VERSION=\"1.5.7\" -fmessage-leng
th=0 -grecord-gcc-switches -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-stron
g -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -g -o ib
is ibissh_wrap.o -Wl,-rpath -Wl,/usr/lib64  -L. -libiscom -L/usr/lib64 -lopensm 
-losmvendor -losmcomp -libumad -ltcl8.6 -ldl -lz -lpthread -lm
[   54s] /usr/lib64/gcc/x86_64-suse-linux/8/../../../../x86_64-suse-linux/bin/ld
: cannot find -libiscom


with -j3 and higher it works.
Same behaviour with --vm-type=kvm .

So there is probably some race (because of insufficient dependencies in Makefiles) that only works out when using more parallelism.