RPaths are basically search paths for how to load dependent libraries.
The order they appear is the order the linker will search, we should
preserve that order in tbd files.

* Additionally add this level of detection to llvm-readtapi.

resolves: rdar://145603347

It matches up with other _attribute_ adding member functions and helps
simplify InterfaceFile assignment for InstallAPI.

A distinction that doesn't _usually_ matter is that the
MachO::SymbolKind is really a mapping of entries in TBD files not
symbols. To better understand this, rename the enum so it represents an
encoding mapped to TBDs as opposed to symbols alone.

For example, it can be a bit confusing that "GlobalSymbol" is a enum
value when all of those values can represent a GlobalSymbol.

… format.

Formats >= TBDv4 will now encode new attribute that the system static
linker wil read when tbd files replace binary dylibs.

Both Swift & LLD use TextAPI reader/writer apis to interface with TBD
files. Add doc strings to document what each API does. Also, add
shortcut APIs for validating input is a TBD file.

This reduces the differences between downstream and how tapi calls into
these APIs.

This adds a new optional flag sim_support which is the same as
MH_SIM_SUPPORT in the MachO header.

Reviewed By: ributzka

Differential Revision: https://reviews.llvm.org/D157433

The minOS version is recorded in tbd-v5 so the linker can report
diagnostics when a library and client are misconfigured.

Dylibs should always have a minOS recorded, but in was not recorded in
previous TBD versions. To accommodate the format transition, treat
unrecorded minOS versions as 0.

Reviewed By: zixuw

Differential Revision: https://reviews.llvm.org/D156487