[stdlib] Fix the OpenBSD modulemap.

[3405691582]

stdint.h is missing; this repairs a number of unit tests.

[gottesmm]

@3405691582 which tests.

[CodaFi]

@swift-ci smoke test and merge

[3405691582]

@gottesmm Affected tests

Swift(openbsd-amd64) :: ClangImporter/enum-cxx.swift
Swift(openbsd-amd64) :: ClangImporter/cxx_interop.swift
Swift(openbsd-amd64) :: ClangImporter/cxx_interop_ir.swift

Swift(openbsd-amd64) :: Interop/Cxx/class/member-variables-typechecker.swift
Swift(openbsd-amd64) :: Interop/C/function/emit-called-inline-function-irgen.swift
Swift(openbsd-amd64) :: Interop/Cxx/class/access-specifiers-typechecker.swift
Swift(openbsd-amd64) :: Interop/Cxx/class/member-variables-module-interface.swift
Swift(openbsd-amd64) :: Interop/Cxx/class/memory-layout-silgen.swift
Swift(openbsd-amd64) :: Interop/Cxx/class/memory-layout-execution.swift
Swift(openbsd-amd64) :: Interop/Cxx/class/access-specifiers-module-interface.swift