package/lvm2: disable parallel build

Parallel build is broken since bump to version 2.03.12 in commit
80997acd. Commits 4526078d, 8a313b01, and a7186cd1 tried to fix
that by only installing systemd units when appropriate.

It turns out that there are more cases where parallel build still fails:

    http://autobuild.buildroot.org/results/995/995f46ee0033e34261ba7b24b61c41e7a088602b/

    >>> lvm2 2.03.12 Installing to staging directory
    [...]
        [INSTALL] ioctl/libdevmapper.so
        [CC] dmsetup.c
    /usr/bin/make -C lib install_device-mapper
        [CC] dmsetup.c
    [...]
        [CC] dmsetup
        [CC] dmsetup
    /nvme/rc-buildroot-test/scripts/instance-0/output-1/host/lib/gcc/arm-buildroot-linux-gnueabihf/10.3.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: /nvme/rc-buildroot-test/scripts/instance-0/output-1/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/Scrt1.o: in function `_start':
    (.text+0x54): undefined reference to `main'
    collect2: error: ld returned 1 exit status
    Makefile:60: recipe for target 'dmsetup' failed

Or:

    http://autobuild.buildroot.org/results/a4e/a4ea87da502272dc2e677123b6fbcb0c23106f0b/

    >>> lvm2 2.03.12 Installing to staging directory
    [...]
        [CC] dmsetup
    /home/giuliobenetti/autobuild/run/instance-3/output-1/host/lib/gcc/arm-buildroot-linux-musleabihf/9.3.0/../../../../arm-buildroot-linux-musleabihf/bin/ld: /home/giuliobenetti/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-musleabihf/sysroot/lib/Scrt1.o: in function `_start_c':
    Scrt1.c:(.text._start_c+0x5c): undefined reference to `main'
    collect2: error: ld returned 1 exit status
    make[3]: *** [Makefile:61: dmsetup] Error 1
    make[3]: Leaving directory '/home/giuliobenetti/autobuild/run/instance-3/output-1/build/lvm2-2.03.12/libdm/dm-tools'
    make[2]: *** [../libdm/make.tmpl:315: dm-tools.device-mapper] Error 2
    make[2]: *** Waiting for unfinished jobs....
        [CC] dmsetup
        [INSTALL] dmsetup
    [...]

Similar traces in either case: it tries to build dmsetup twice, at
intall time instead of build time.

Fixes:
  - http://autobuild.buildroot.org/results/995/995f46ee0033e34261ba7b24b61c41e7a088602b/
  - http://autobuild.buildroot.org/results/a4e/a4ea87da502272dc2e677123b6fbcb0c23106f0b/



Note that this is just a workaround for a broken buildsystem anyway:
indeed, the build of dmsetup is done at install time, instead of build
time. More fixes should be worked on with upstream to properly fix the
issue...

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr:
  - update after the three partial fix-commits
  - extend commit log accordingly
  - add new upstream failures
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>