For clients, such as the debugger, who do not have access the full
output of the dependency scanner, it is a huger performance and
correctness improvement if each explicitly built Swift module not just
serialized all its Clang .pcm dependencies (via the serialized Clang
compiler invocation) but also its direct Swift module dependencies.
This patch changes the Swift module format to store the absolute path
or cas cache key for each dependency in the INPUT block, and makes
sure the deserialization makes these available to the ESML.
rdar://150969755
Add function to handle all macro dependencies kinds in the scanner,
including taking care of the macro definitions in the module interface
for its client to use. The change involves:
* Encode the macro definition inside the binary module
* Resolve macro modules in the dependencies scanners, including those
declared inside the dependency modules.
* Propagate the macro defined from the direct dependencies to track
all the potentially available modules inside a module compilation.
