build: allow unified builds on Windows

We cannot query the location of the clang target when clang is built in
a unified build.  Use a generator expression instead.

Author: compnerd

CMakeLists.txt

@@ -968,17 +968,14 @@ if(SWIFT_NEED_EXPLICIT_LIBDISPATCH)
     set(SWIFT_LIBDISPATCH_C_COMPILER ${CMAKE_C_COMPILER})
     set(SWIFT_LIBDISPATCH_CXX_COMPILER ${CMAKE_CXX_COMPILER})
   elseif(${CMAKE_SYSTEM_NAME} STREQUAL ${CMAKE_HOST_SYSTEM_NAME})
-    get_target_property(CLANG_LOCATION clang LOCATION)
-    get_filename_component(CLANG_LOCATION ${CLANG_LOCATION} DIRECTORY)
-
     if(CMAKE_SYSTEM_NAME STREQUAL Windows)
       set(SWIFT_LIBDISPATCH_C_COMPILER
-          ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+          $<TARGET_FILE_DIR:clang>/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
       set(SWIFT_LIBDISPATCH_CXX_COMPILER
-          ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+          $<TARGET_FILE_DIR:clang>/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
     else()
-      set(SWIFT_LIBDISPATCH_C_COMPILER ${CLANG_LOCATION}/clang)
-      set(SWIFT_LIBDISPATCH_CXX_COMPILER ${CLANG_LOCATION}/clang++)
+      set(SWIFT_LIBDISPATCH_C_COMPILER $<TARGET_FILE_DIR:clang>/clang)
+      set(SWIFT_LIBDISPATCH_CXX_COMPILER $<TARGET_FILE_DIR:clang>/clang++)
     endif()
   else()
     message(SEND_ERROR "libdispatch requires a newer clang compiler (${CMAKE_C_COMPILER_VERSION} < 3.9)")

cmake/modules/SwiftWindowsSupport.cmake

@@ -84,20 +84,19 @@ endfunction()
 macro(swift_swap_compiler_if_needed target)
   if(NOT CMAKE_C_COMPILER_ID MATCHES Clang)
     if(CMAKE_SYSTEM_NAME STREQUAL CMAKE_HOST_SYSTEM_NAME)
-      get_target_property(CLANG_LOCATION clang LOCATION)
-      get_filename_component(CLANG_LOCATION ${CLANG_LOCATION} DIRECTORY)
-
-      if("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC" OR
-          "${CMAKE_C_SIMULATE_ID}" STREQUAL "MSVC")
-        set(CMAKE_C_COMPILER
-          ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
-        set(CMAKE_CXX_COMPILER
-          ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+      get_target_property(IMPORTED clang IMPORTED)
+      if(IMPORTED)
+        set(CLANG_LOCATION $<TARGET_FILE_DIR:clang>)
       else()
-        set(CMAKE_C_COMPILER
-          ${CLANG_LOCATION}/clang${CMAKE_EXECUTABLE_SUFFIX})
-        set(CMAKE_CXX_COMPILER
-          ${CLANG_LOCATION}/clang++${CMAKE_EXECUTABLE_SUFFIX})
+        set(CLANG_LOCATION ${LLVM_RUNTIME_OUTPUT_INTDIR})
+      endif()
+
+      if("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_C_SIMULATE_ID}" STREQUAL "MSVC")
+        set(CMAKE_C_COMPILER ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+        set(CMAKE_CXX_COMPILER ${CLANG_LOCATION}/clang-cl${CMAKE_EXECUTABLE_SUFFIX})
+      else()
+        set(CMAKE_C_COMPILER ${CLANG_LOCATION}/clang${CMAKE_EXECUTABLE_SUFFIX})
+        set(CMAKE_CXX_COMPILER ${CLANG_LOCATION}/clang++${CMAKE_EXECUTABLE_SUFFIX})
       endif()
     else()
       message(SEND_ERROR "${target} requires a clang based compiler")