[SR-9368] libdispatch_static unit tests are disabled

[kevints]

Previous ID	SR-9368
Radar	None
Original Reporter	@kevints
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	libdispatch
Labels	Bug
Assignee	None
Priority	Medium

md5: 30b402df2ea7747770589550544f234d

relates to:

• SR-10625 tests for -static-*
• SR-7039 can't use -static-stdlib (or -static-executable) with any Dispatch using app

Issue Description:

swiftlang/swift#20793 introduced a libdispatch_static product to the build script but doesn't run its unit tests. To ensure code quality we should make sure the unit tests pass on this path as well.

[belkadan]

cc @compnerd

To be "fair" I don't think we're testing the static stdlib properly either.