[Flang][RISCV] Emit target features for RISC-V

Fix the issue of .o file generated by `Flang`
with `Flags` info is 0x0 under RISC-V.

Reviewed By: awarzynski, kiranchandramohan

Differential Revision: https://reviews.llvm.org/D145883
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 84d93f5..10a518c 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -105,7 +105,7 @@
   default:
     break;
   case llvm::Triple::aarch64:
-    [[fallthrough]];
+  case llvm::Triple::riscv64:
   case llvm::Triple::x86_64:
     getTargetFeatures(D, Triple, Args, CmdArgs, /*ForAs*/ false);
     break;