common: fix few tests to work under bullseye

Fix execute tests under coverage tool bullseye:
-vmem_valgrind
-blk_nblock
-blk_rw
blk: check return value of pthread_mutex_unlock()
build: ensure ld can find libpmem during build
blk: add checking number and size of internal lbas in each arena
benchmarks: fix pread and pwrite

On some systems the pread and pwrite calls are not declared
due to lack of appropriate feature test macro.
Define __USE_UNIX98 before including unistd.h in order to turn on
pread and pwrite declarations.
Merge pull request #46 from plebioda/fix-pread-pwrite

benchmarks: fix pread and pwrite
Merge pull request #45 from ldorau/blk-check-return-value

blk: check return value of pthread_mutex_unlock()
Merge pull request #44 from tomaszkapela/pmemblk-fix-excessive-block-size

blk: add checking number and size of internal lbas in each arena
Merge pull request #37 from spawlows/fix-test-under-bullseye

common: fix few tests to work under bullseye
vmem: fix format string
common: add NVML magic file

- create NVML magic script for file(1) command
- install NVML magic script with rpm and dpkg packages
vmem: do not unlock ctl_mtx mutex twice

The ctl_mtx mutex is unlocked at src/jemalloc/src/ctl.c:785.
common: prevent compilation for 32-bit platforms

32/64-bit detection added to makefile.
Compilation stops with a clear error message, if user attempts to
build NVML for 32-bit.
Merge pull request #47 from ldorau/vmem-fix-ctl_mtx-mutex

vmem: do not unlock ctl_mtx mutex twice
Merge pull request #48 from plebioda/nvml-magic-file

common: add NVML magic file
Merge pull request #49 from krzycz/common-prevent_32bit_compilation

common: prevent compilation for 32-bit platforms
Merge pull request #50 from krzycz/common-print_formats1

vmem: fix format string
blk: fix external_nlba size in struct arena
Merge pull request #51 from plebioda/btt-fix-arena-external-nlba-size

blk: fix external_nlba size in struct arena