This is the first patch implementing the new Flang driver as outlined in ,
 & . It created Flang driver (flang-new and Flang frontend driver
(flang-new -fc1) with help screen(-help) and version(--version) options.
These will be renamed as flang and flang -fc1 once the current Flang
throwaway driver, flang, can be replaced
flang-new is implemented in terms of libclangDriver, defaulting the driver
mode to flang (added to libclangDriver in ). This ensures that the driver
runs in flang mode regardless of the name of the binary inferred from argv.
The design of the new flang compiler and frontend drivers is inspired by it
counterparts in Clang . Currently, the new flang compiler and frontend
drivers re-use Clang libraries: clangBasic, clangDriver and clangFrontend.
To identify Flang options, this patch adds FlangOption enum. printHelp is
updated so that flang-new prints only Flang options.
The new Flang driver is disabled by default. To build it, set
-DBUILD_FLANG_NEW_DRIVER =ON when configuring Flang and LLVM_ENABLE_PROJECTS
 RFC: new Flang driver - next steps
 "RFC: Adding a fortran mode to the clang driver for flang"
RFC: refactoring libclangDriver/libclangFrontend to share with Flan