[CMake] Better dependency checking

Author: davezarzycki

CMakeLists.txt

@@ -509,6 +509,8 @@ message(STATUS "C Compiler (${CMAKE_C_COMPILER}) Version: ${CMAKE_C_COMPILER_VER
 message(STATUS "C++ Compiler (${CMAKE_CXX_COMPILER}) Version: ${CMAKE_CXX_COMPILER_VERSION}")
 if (CMAKE_Swift_COMPILER)
   message(STATUS "Swift Compiler (${CMAKE_Swift_COMPILER}) Version: ${CMAKE_Swift_COMPILER_VERSION}")
+elseif (SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER)
+  message(FATAL_ERROR "Swift Compiler not found and SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER is set")
 else()
   message(STATUS "Swift Compiler (None).")
 endif()

stdlib/cmake/modules/SwiftSource.cmake

@@ -643,7 +643,7 @@ function(_compile_swift_files
   endif()
 
   set(swift_compiler_tool_dep)
-  if(SWIFT_INCLUDE_TOOLS)
+  if(SWIFT_INCLUDE_TOOLS AND NOT SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER)
     # Depend on the binary itself, in addition to the symlink.
     set(swift_compiler_tool_dep "swift-frontend")
   endif()