- Allow 0 to be a valid value pruning interval in C LTO API. Value 0 will cause garbage collector to run. This matches the behavior in C++ LTO API.
- Updated comments accordingly.
- Updated the default value of pruning interval to be 1200 second in llvm-lto; that corresponds to the default values for all other users of C/C++ LTO API. This change is optional and could be reverted if there are some objections.
If someone knows (Mehdi?) the name of the person who works on ThinLTO in Apple, it will be nice to add him as a reviewer, since this is a change in C LTO API.