Add explicit dependency on absl for xrt_swemu abd xrt_hwemu targets

[unsatcore]

Problem solved by the commit

Fixes linkage of xrt_swemu and xrt_hwemu targets from runtime_src/core/pcie/emulation/

Bug / issue (if any) fixed, which PR introduced the bug, how it was discovered

Mentioned components won't link on NixOS 23.11 (gcc 13.2.0, cmake 3.28.3):

...
/nix/store/...-binutils-2.41/bin/ld: /nix/store/...-protobuf-24.4/include/google/protobuf/repeated_ptr_field.h:704:(.text._ZN6google8protobuf8internal20RepeatedPtrFieldBase13ClearNonEmptyINS0_16RepeatedPtrFieldI45xclPerfMonReadTrace_Streaming_response_eventsE11TypeHandlerEEEvv[_ZN6google8protobuf8internal20RepeatedPtrFieldBase13ClearNonEmptyINS0_16RepeatedPtrFieldI45xclPerfMonReadTrace_Streaming_response_eventsE11TypeHandlerEEEvv]+0xc1): undefined reference to `absl::lts_20240116::log_internal::LogMessageFatal::~LogMessageFatal()
...

claiming undefined references to abseil-cpp library.

Corresponding CMakeFiles/xrt_[s|h]wemu.dir/link.txt files won't mention absl either.

How problem was solved, alternative solutions (if any) and why they were rejected

Explicit dependency on absl::log and absl::check was introduced into relevant CMakeLists.txt files

I'm aware NixOS is not supported, still not sure how this even works on Ubuntu / RHEL.
Hopefully being a bit more clear re dependencies won't hurt.

Risks (if any) associated the changes in the commit

The commit was not tested on any of the officially supported distros

What has been tested and how, request additional testing if necessary

The build was only tested locally.
It is required to make sure the build passes on all the supported systems.

Documentation impact (if any)

None

[gbuildx]

unsatcore - is not a collaborator
Can XRT admins please validate PR

[gbuildx]

Can one of the admins verify this patch?

[stsoe]

Where is CMake supposed to find absl from? This change doesn't look like it will work.
Please make this change work on variants of Linux supported by XRT.