[NVPTX] Add NVPTXCtorDtorLoweringPass to handle global ctors / dtors

This patch mostly adapts the existing AMDGPUCtorDtorLoweringPass for use
by the Nvidia backend. This pass transforms the ctor / dtor list into a
kernel call that can be used to invoke those functinos. Furthermore, we
emit globals such that the names and addresses of these constructor
functions can be found by the driver. Unfortunately, since NVPTX has no
way to emit variables at a named section, nor a functioning linker to
provide the begin / end symbols, we need to mangle these names and have
an external application find them.

This work is related to the work in D149398 and D149340.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D149451