detect GDB and disable tests

ref issue #469

Backport hash map erase fix to stable 1.8

Consider the following scenario (where A and B are in the same bucket):
thread 1:		thread 2:
find(acc1, A)
			erase(A)
find(acc2, B)

First, thread 1 takes lock on the bucket and then on element A.
Then, thread 2 takes a lock on the bucket and tries to lock element A
but it can't because thread 1 already locked it - this way thread 2 is blocked.
Next, thread 1 tries to lock the bucket but it can't because thread 2 holds it.
Neither thread can progress.

This patch fixes that by introducing the same algorithm as in lookup/insert.
When trying to lock element in erase we now spin in a loop doing try_acquire and
if we do not succeed after specified amount of time we drop bucket lock and try
whole operation again.

Merge stable 1.7 into stable 1.8

Fix overrding TEST_DIR variable

TEST_DIR is used to specify location of test artifacts. It can NOT
be overwritten.

Add missing pmdk-debuginfo rpms installation

Merge changes from stable-1.6

tests: remove unnecessary #include <libpmemobj.h>

Merge changes from stable-1.5

allocator: remove unnecessary #include <libpmemobj.h>

Including libpmemobj.h causes inclusion of all type macros
which are not needed by C++.

Including libpmemobj.h causes inclusion of all type macros
which are not needed by C++.

test: remove concurrent_hash_map_pmreorder_insert_erase_mt test

Multi-threaded tests cannot be run under pmreorder,
because pmreorder does not support multi-threaded tests.

Vs 2019 fixes

Update comment for pool::persist(persistent_ptr&)

Fix finding libpmem and libpmemobj in CMake

Functions modified in this patch do not modify the object so they should be
marked as const.

This fixes compilation on VS 2019.

to initialization list. Every const member (like table_ptr)
should be initialized this way. Failing to do so may result in compilation
error.

Generate the fatal error if any of the required files is not found.

Former description could have been misinterpreted. Persist
operation does not persist pointee but only a pointer - this
change makes that clear.

Ref: https://github.com/pmem/libpmemobj-cpp/issues/524

Implement rehash_bucket using a transaction

And use it for long running tests (concurrent hash map drd tests).

This test aborts application in the middle of rehash operation and
checks consistency after restart.

This fixes problem with inconsistent state after crash. In previous implementation
if application crashed in the middle of rehash it was possible that two buckets
(old and new) pointed to the same element. This meant that size could be too big
(some elements could be counted twice). Putting all operations which change list
pointers inside of a transction solves this issue and eliminates requirement
to have 'restore_after_crash' logic.

set_rehashed is done outside of a transaction because otherwise:
- on abort rehashed flag would be rolled back by obj using memcpy instead of
  std::atomic API which could be UB
- some thread could check for rehashed flag and decide that rehash is not needed
  but after that transaction could abort and move elements back

Fail concurrent_hash_map drd/helgrind tets on non-pmem

Add option to enable concurrent_hash_map drd and helgrind tests.
If this option is enabled and TEST_DIR points to non-pmem fail
tests which require pmem and print appropriate error message.

Some tests and examples require clang >= 8.0

Fix installing libpmem-*.rpm

Fix removing pkg-config rpm package