[test] Fix line-directive on Windows

Author: stevapple

stdlib/cmake/modules/SwiftSource.cmake

@@ -640,7 +640,12 @@ function(_compile_swift_files
   endif()
 
   set(line_directive_tool "${SWIFT_SOURCE_DIR}/utils/line-directive")
-  set(swift_compiler_tool "${SWIFT_NATIVE_SWIFT_TOOLS_PATH}/swiftc")
+  # line-directive needs full path on Windows.
+  if (CMAKE_SYSTEM_NAME STREQUAL Windows)
+    set(swift_compiler_tool "${SWIFT_NATIVE_SWIFT_TOOLS_PATH}/swiftc.exe")
+  else()
+    set(swift_compiler_tool "${SWIFT_NATIVE_SWIFT_TOOLS_PATH}/swiftc")
+  endif()
   set(swift_compiler_tool_dep)
   if(SWIFT_INCLUDE_TOOLS)
     # Depend on the binary itself, in addition to the symlink.