[cmake] Add option for running tests against a just built toolchain.

The option is specifically: SWIFT_RUN_TESTS_WITH_HOST_COMPILER. NOTE: We assume
that swiftc is in the just built toolchain directory and all necessary tools are
next to swiftc.

I am using this to bring up tests for a stage2 swift stdlib build (and eventual
libswift support).

Author: gottesmm

CMakeLists.txt

@@ -250,6 +250,10 @@ option(SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER
        "Use the host compiler and not the internal clang to build the swift runtime"
        FALSE)
 
+option(SWIFT_RUN_TESTS_WITH_HOST_COMPILER
+       "Run tests against the host compiler and not the just built swift"
+       FALSE)
+
 set(SWIFT_SDKS "" CACHE STRING
     "If non-empty, limits building target binaries only to specified SDKs (despite other SDKs being available)")
 

test/CMakeLists.txt

@@ -134,10 +134,20 @@ set(SWIFT_LIT_ARGS "" CACHE STRING "Arguments to pass to lit")
 set(SWIFT_LIT_ENVIRONMENT "" CACHE STRING "Environment to use for lit invocations")
 
 if(NOT SWIFT_INCLUDE_TOOLS)
-  list(APPEND SWIFT_LIT_ARGS
-       "--path=${SWIFT_NATIVE_LLVM_TOOLS_PATH}"
-       "--path=${SWIFT_NATIVE_CLANG_TOOLS_PATH}"
-       "--path=${SWIFT_NATIVE_SWIFT_TOOLS_PATH}")
+  if(SWIFT_RUN_TESTS_WITH_HOST_COMPILER)
+    precondition(CMAKE_Swift_COMPILER MESSAGE "Can only run tests if a Swift compiler is specified")
+    get_filename_component(SWIFT_COMPILER_DIR "${CMAKE_Swift_COMPILER}" DIRECTORY)
+    precondition(SWIFT_COMPILER_DIR)
+    # We assume that we are building against a toolchain where all tools are
+    # next to swiftc.
+    list(APPEND SWIFT_LIT_ARGS
+      "--path=${SWIFT_COMPILER_DIR}")
+  else()
+    list(APPEND SWIFT_LIT_ARGS
+      "--path=${SWIFT_NATIVE_LLVM_TOOLS_PATH}"
+      "--path=${SWIFT_NATIVE_CLANG_TOOLS_PATH}"
+      "--path=${SWIFT_NATIVE_SWIFT_TOOLS_PATH}")
+  endif()
   if(SWIFT_BUILD_STDLIB)
     list(APPEND SWIFT_LIT_ARGS
          "--param" "test_resource_dir=${SWIFTLIB_DIR}")