[cmake] Enable users to specify archive creation commands

This diff enables users to override CMAKE_C_ARCHIVE_CREATE & CMAKE_CXX_ARCHIVE_CREATE
(currently set in HandleLLVMOptions.cmake).

For example, one can specify
cmake -DCMAKE_C_ARCHIVE_CREATE="<CMAKE_AR> TDqc <TARGET> <LINK_FLAGS> <OBJECTS>" \
      -DCMAKE_CXX_ARCHIVE_CREATE="<CMAKE_AR> TDqc <TARGET> <LINK_FLAGS> <OBJECTS>" ...
to make the build create thin archives instead of regular ones.
For a clean run `ninja lld` using thin archives seems to reduce the size
of the build directory from ~14GB to ~8GB

Differential revision: https://reviews.llvm.org/D116850