[clang][ssaf] Implement Entity Linker CLI and patching for JSON Format
This PR implements Entity ID patching for the JSON serialization format
and introduces `ssaf-linker`, a command-line tool that drives the
`EntityLinker`.
1. Entity ID references inside summary blobs use the sentinel
representation `{"@": <uint64>}`. Patching walks the JSON value tree
recursively, recognizes sentinels, and rewrites their indices using the
`EntityResolutionTable` provided by the linker.
2. An object with an `@` key but extra keys `(size != 1)`, an `@` value
that is not a valid `uint64`, and an entity ID not present in the
resolution table, lead to patching errors.
3. `JSONFormat::EntityIdConverter` is replaced with two `function_ref`
typedefs to eliminate the wrapper class.
4.`ssaf-linker` is implemented in `clang/tools/ssaf-linker/` and gets
built at `bin/ssaf-linker`.
5. lit tests check CLI, verbose output, timing output, validation
errors, I/O errors, linking errors, and successful linking.
rdar://162570931
sysutils/rubygem-ohai18: Update RUN_DEPENDS
- Change RUN_DEPENDS from rubygem-chef-config to rubygem-chef-config18
- Change RUN_DEPENDS from rubygem-chef-utils to rubygem-chef-utils18
- Bump PORTREVISION for dependency change
