[SR-10804] Add $(inherited) to OTHER_SWIFT_FLAGS

[aciidgh]

Previous ID	SR-10804
Radar	rdar://problem/50768026
Original Reporter	@aciidb0mb3r
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Package Manager
Labels	Bug, StarterBug
Assignee	@aciidb0mb3r
Priority	Medium

md5: 97a805b3eb82159998ed8f3a2f80fee9

Issue Description:

Add `$(inherited)` to the list of `OTHER_SWIFT_FLAGS` in swift package generate-xcodeproj. At the moment if there are some other defines in `OTHER_SWIFT_FLAGS`, they are overwritten by the xcodeproj with just a `-DXcode` flag.

[belkadan]

Still working on this, drewcyborg (JIRA User)?

(I'm checking in on all the StarterBugs that haven't been touched in over a month; it's totally fine if you just haven't had time but still want to keep it.)

[aciidgh]

#2193 master
#2194 swift-5.1-branch