Other implementations of the symbol graph format use zero-based indices
for source locations, which causes problems when combined with clang's
current one-based indices. This commit sets ExtractAPI's symbol graph
output to use zero-based indices to align with other implementations.
rdar://107639783
This Patch gives ExtractAPI the ability to emit correct availability information for symbols marked as unavailable on a specific platform ( PR#60954 )
Reviewed By: dang
Differential Revision: https://reviews.llvm.org/D144940
Currently ExtractAPI only emits availability information for the
current platform. This makes it easy for clients to get all availability
information for a given symbol in one invocation as opposed to having to invoke
clang once per-platform and then merge the symbol-graphs.
Differential Revision: https://reviews.llvm.org/D130918
