[6.0.2][CMake] Explicitly link Testing to Foundation (#713)

Cherry-pick #693 into `release/6.0.2`

* **Explanation**: Previously in CMake builds, when `Foundation` was not
in the regular search directory (e.g. resource directory or SDK search
paths) `#if canImport(Foundation)` used to fail, and the functionalities
are not included. This patch provides a way to provide `Foundation_DIR`
for `find_packgage(Foundation CONFIG)`, so that clients can correctly
link Testing to Foundation
* **Scope**: CMake builds
* **Risk**: Low. No actual code changes.
* **Testing**: Passes current test suite Also manually tested the build
toolchain
* **Issues**: N/A
* **Reviewer**: @stmontgomery

---------

Co-authored-by: Jonathan Grynspan <jgrynspan@apple.com>

CMakeLists.txt

@@ -15,6 +15,13 @@ endif()
 project(SwiftTesting
   LANGUAGES CXX Swift)
 
+if(NOT APPLE)
+  if(NOT CMAKE_SYSTEM_NAME STREQUAL WASI)
+    find_package(dispatch CONFIG)
+  endif()
+  find_package(Foundation CONFIG)
+endif()
+
 include(GNUInstallDirs)
 
 list(APPEND CMAKE_MODULE_PATH

Sources/Testing/CMakeLists.txt

@@ -94,6 +94,14 @@ add_library(Testing
   Traits/Trait.swift)
 target_link_libraries(Testing PRIVATE
   _TestingInternals)
+if(NOT APPLE)
+  if(NOT CMAKE_SYSTEM_NAME STREQUAL WASI)
+    target_link_libraries(Testing PUBLIC
+      dispatch)
+  endif()
+  target_link_libraries(Testing PUBLIC
+    Foundation)
+endif()
 if(NOT BUILD_SHARED_LIBS)
   # When building a static library, tell clients to autolink the internal
   # library.