1495: fix Alpine build

[cz4rs]

fixes #1495

Fixes the stack dumping issues with Alpine build by replacing libexecinfo with libunwind.
Does a minor cleanup of our backtrace-generating code as well.

---

cc52339 is the simplest workaround to the failing test - it just disables stack printing. I will try to come up with an actual fix.
Confirmed that it works with:

ctest --output-on-failure --repeat-until-fail 100 -R TestMpiAccessGuardDeathTest.test_mpi_access_prevented_proc_2

(unfixed version crashes every couple of runs).

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PR tests (gcc-6, ubuntu, mpich)

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PR tests (clang-3.9, ubuntu, mpich)

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PR tests (gcc-5, ubuntu, mpich)

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PR tests (gcc-9, ubuntu, mpich, zoltan)

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PR tests (clang-5.0, ubuntu, mpich)

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PR tests (gcc-10, ubuntu, openmpi, no LB)

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PR tests (gcc-8, ubuntu, mpich, address sanitizer)

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PR tests (nvidia cuda 10.1, ubuntu, mpich)

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PR tests (clang-9, ubuntu, mpich)

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PR tests (clang-10, alpine, mpich)

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PR tests (nvidia cuda 11.0, ubuntu, mpich)

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PR tests (clang-10, ubuntu, mpich)

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[github-actions]

PR tests (gcc-7, ubuntu, mpich, trace runtime, LB)

Build for 1cf2b68

FAILED: tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx.o 
/usr/bin/ccache /usr/bin/g++ -DJSON_USE_IMPLICIT_CONVERSIONS=1 -DVT_NO_COLOR_ENABLED -I/vt/tests/unit -I/vt/lib/CLI -I/vt/lib/json/include -I/vt/lib/brotli/c/include -I/vt/lib/libfort/lib -Irelease -I/vt/src -isystem /vt/tests/extern/googletest/googletest/include -isystem /vt/tests/extern/googletest/googletest -isystem /vt/lib/fmt/include -isystem /vt/lib/EngFormat-Cpp/include -isystem /build/checkpoint/install/include -isystem /build/detector/install/include -O3 -DNDEBUG -fdiagnostics-color=always -Wall -pedantic -Wshadow -Wno-unknown-pragmas -Wsign-compare -ftemplate-backtrace-limit=100 -Werror -O0 -g --coverage -fPIC -std=c++14 -MD -MT tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx.o -MF tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx.o.d -o tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx.o -c tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx
In file included from tests/CMakeFiles/configs_basic.dir/Unity/unity_0_cxx.cxx:4:0:
/vt/tests/unit/configs/test_stack_dumping.cc:48:10: fatal error: vt/configs/error/pretty_print_stack.h: No such file or directory
 #include "vt/configs/error/pretty_print_stack.h"
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Build log

[codecov]

Codecov Report

Merging #1657 (467bc11) into develop (46b2db0) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 467bc11 differs from pull request most recent head e09fc43. Consider uploading reports for the commit e09fc43 to get more accurate results

@@           Coverage Diff            @@
##           develop    #1657   +/-   ##
========================================
  Coverage    83.44%   83.44%           
========================================
  Files          800      800           
  Lines        30922    30923    +1     
========================================
+ Hits         25803    25805    +2     
+ Misses        5119     5118    -1     

Impacted Files	Coverage Δ
src/vt/sequence/seq_node.cc	85.71% <0.00%> (+0.47%)	⬆️
src/vt/configs/error/stack_out.cc	70.00% <0.00%> (+1.03%)	⬆️

[cz4rs]

Related bug report in Alpine's GitLab:
https://gitlab.alpinelinux.org/alpine/aports/-/issues/10896

[cz4rs]

TODO:

• expand 5a33c27 to handle errors correctly (mostly early returns)
• handle introduced FIXMEs
  • use find_package to locate libunwind (?) - only if deemed necessary, note that there is no official CMake module for this
• investigate the errors in TestPreconfig.test_vt_assert and TestCliArguments.test_vt_assert
  • some of the clang/ubuntu builds were segfaulting
  • just linking libunwind was enough for the segfaults to occur (even without calling any functions)
  • the solution was to build libunwind on our own instead of using default Ubuntu package

[PhilMiller]

It looks like this is going to cause trouble for EMPIRE, at least as is - I just imported current vt to test #1683, and found that the build failed to find libunwind.h. Should we be vendoring it into our lib/ directory?