[flang][driver] Add support for generating LLVM bytecode files

Support for generating LLVM BC files is added in Flang's compiler and
frontend drivers. This requires the `BitcodeWriterPass` pass to be run
on the input LLVM IR module and is implemented as a dedicated frontend
aciton. The new functionality as seen by the user (compiler driver):
```
flang-new -c -emit-llvm file.90
```
or (frontend driver):
```
flang-new -fc1 -emit-llvm-bc file.f90
```

The new behaviour is consistent with `clang` and `clang -cc1`.

Differential Revision: https://reviews.llvm.org/D123211

1 files changed, 3 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index d1f427a..ea5accd7 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -148,6 +148,9 @@ static bool ParseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     case clang::driver::options::OPT_emit_llvm:
       opts.programAction = EmitLLVM;
       break;
+    case clang::driver::options::OPT_emit_llvm_bc:
+      opts.programAction = EmitLLVMBitcode;
+      break;
     case clang::driver::options::OPT_emit_obj:
       opts.programAction = EmitObj;
       break;