This patch is motivated by (and factored out from) https://reviews.llvm.org/D66121 which is a debug info bugfix. Starting with DWARF 5 all Objective-C methods are nested inside their containing type, and that patch implements this for synthesized Objective-C properties.
This patch became much longer than I hoped it would be but most of the changes are mechanical in nature.
- SemaObjCProperty populates a list of synthesized accessors that may need to inserted into an ObjCImplDecl.
- SemaDeclObjC::ActOnEnd inserts forward-declarations for all accessors for which no override was provided into their ObjCImplDecl. This patch does *not* synthesize AST function *bodies*. Moving that code from the static analyzer into Sema may be a good idea though.
- Places that expect all methods to have bodies have been updated.
Most of the updates are very straightforward, the most irritating part was updating the static analyzer, there may be a more elegant way to do this.
I'm somewhat concerned that I didn't have to update the GNU Objective-C runtime for the testsuite to pass. I did not update the static analyzer's inliner for synthesized properties to point back to the property declaration (see test/Analysis/Inputs/expected-plists/nullability-notes.m.plist), which I believed to be more bug than a feature.