Forward our target from the driver to Clang

This will allow us to use Clang independently of its default build target, as long as our target is supported. Issue: eng/toolchain/llvm-project#29

Author: sebastianpoeplau

llvm-interface/gcc_wrapper.adb

@@ -65,7 +65,7 @@ procedure GCC_Wrapper is
  -- is a Clang instance that we expect to be on the PATH, like GNAT-LLVM C.
 
  GCC : constant String := Command_Name;
- Args : Argument_List (1 .. Argument_Count + 1);
+ Args : Argument_List (1 .. Argument_Count + 2);
  Arg_Count : Natural := 0;
  Status : Boolean;
  Last : Natural;
@@ -314,7 +314,7 @@ begin
  null;
 
  elsif Arg = "-x" then
- if J < Args'Last then
+ if J < Argument_Count then
 
  -- While we can use our embedded Clang ("llvm-helper") to
  -- compile assembly code, we need to forward C and C++ code to
@@ -438,6 +438,14 @@ begin
  return;
  end if;
 
+ -- Tell Clang which target to compile or link for
+
+ if Compiler /= Ada_Frontend or else not Compile then
+ Args (Arg_Count + 1) := new String'("-target");
+ Args (Arg_Count + 2) := new String'(Default_Target_Triple);
+ Arg_Count := Arg_Count + 2;
+ end if;
+
  -- Compile c/c++ files with clang
 
  if Compiler = Bundled_Clang or else Compiler = External_Clang then