check_so_deps: remove the SPDK_NO_LIB_DEPS variable

This variable used to control whether the dependencies of a .so library
were listed during linking.  But the way confirm_makefile_deps() works
is it builds a list of dependencies by going through each undefined
symbol in a library, finding the library that defines that symbol, and
then comparing that list to the list from mk/spdk.lib_deps.mk.  It
doesn't matter whether any of those libraries were linked in or not.

The only difference, in terms of confirm_makefile_deps(), setting this
variable makes is that the undefined symbols have their type filled in
properly:

w/o SPDK_NO_LIB_DEPS:
Num:    Value          Size Type    Bind   Vis      Ndx Name
  0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
  1: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND spdk_dif_ctx_set_data_offset
  2: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND spdk_bdev_comparev_and_writev_blocks
  3: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND spdk_bdev_queue_io_wait
  4: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND free@GLIBC_2.2.5 (2)
  ...

w/ SPDK_NO_LIB_DEPS=1:
Num:    Value          Size Type    Bind   Vis      Ndx Name
  0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
  1: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND spdk_dif_ctx_set_data_offset
  2: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND spdk_bdev_comparev_and_writev_blocks
  3: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND spdk_bdev_queue_io_wait
  4: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND free@GLIBC_2.2.5 (2)
  ...

It required a slight modification to the way we search for the undefined
symbols, but it actually ended up making it a bit simpler.

Another advantage of this change is that it's now possible to run this
test without having to rebuild everything with SPDK_NO_LIB_DEPS=1.

Signed-off-by: Konrad Sztyber <konrad.sztyber@intel.com>
Change-Id: I62c13c7328f9593480c09b858cf575bf621b62eb
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/20846


Community-CI: Mellanox Build Bot
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Michal Berger <michal.berger@intel.com>
Reviewed-by: Ben Walker <ben@nvidia.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>