After a value is consumed, we emit a `debug_value undef` to indicate that the
variable value is no longer valid to the debugger. However, once a value is
reassigned, it becomes valid again, so emit a `debug_value %original_address` to
reassociate the variable with the valid memory location. rdar://109218404
Specifically, I split it into 3 initial categories: IR, Utils, Verifier. I just
did this quickly, we can always split it more later if we want.
I followed the model that we use in SILOptimizer: ./lib/SIL/CMakeLists.txt vends
a macro (sil_register_sources) to the sub-folders that register the sources of
the subdirectory with a global state variable that ./lib/SIL/CMakeLists.txt
defines. Then after including those subdirs, the parent cmake declares the SIL
library. So the output is the same, but we have the flexibility of having
subdirectories to categorize source files.
