build: add dependency on Foundation

Now that Foundation is required for SwiftSyntax, add the ability to tie
together build trees and bootstrap SwiftSyntax.  This is required to
repair the Windows build.

Author: compnerd

CMakeLists.txt

@@ -23,6 +23,9 @@ set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 
 set(CMAKE_MACOSX_RPATH YES)
 
+find_package(dispatch QUIET)
+find_package(Foundation QUIET)
+
 add_subdirectory(Sources)
 
 export(EXPORT SwiftSyntaxTargets

Sources/SwiftSyntaxBuilder/CMakeLists.txt

@@ -27,8 +27,12 @@ target_link_libraries(SwiftSyntaxBuilder PUBLIC
   SwiftBasicFormat
   SwiftParser
   SwiftParserDiagnostics
-  SwiftSyntax
-  )
+  SwiftSyntax)
+if(TARGET Foundation AND TARGET dispatch)
+  target_link_libraries(SwiftSyntaxBuilder PRIVATE
+    $<$<NOT:$<PLATFORM:Darwin>>:dispatch>
+    $<$<NOT:$<PLATFORM:Darwin>>:Foundation>)
+endif()
 
 set_property(GLOBAL APPEND PROPERTY SWIFTSYNTAX_EXPORTS SwiftSyntaxBuilder)