Fix warnings as errors in pedantic mode

[rlalik]

Fix warnings causing errors in pedantic mode and deprecation warnings:

CMake Warning (dev) at build/fix-things/_deps/alpaca-src/CMakeLists.txt:14 (string):
  uninitialized variable 'CMAKE_LIBRARY_ARCHITECTURE'
This warning is for project developers.  Use -Wno-dev to suppress it.

for tests:

CMake Deprecation Warning at test/CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.