Revert "Turning off clang-link-flang option by default" (llvm#3101)

Author: ronlieb

clang/tools/driver/CMakeLists.txt

@@ -79,7 +79,7 @@ endif()
 
 add_dependencies(clang clang-resource-headers)
 
-option(CLANG_LINK_FLANG "Create flang install link to clang" OFF)
+option(CLANG_LINK_FLANG "Create flang install link to clang" ON)
 if(NOT CLANG_LINKS_TO_CREATE)
   if(CLANG_LINK_FLANG)
     set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp flang)