Generate binemit::emit_inst() functions.

Use the meta language encoding recipes to generate an emit_inst()
function for each ISA. The generated calls into recipe_*() functions
that must be implemented by hand.

Implement recipe_*() functions for the RISC-V recipes.

Add the TargetIsa::emit_inst() entry point which emits an instruction to
a CodeSink trait object.

lib/cretonne/meta/build.py

@@ -12,6 +12,7 @@ import gen_build_deps
 import gen_encoding
 import gen_legalizer
 import gen_registers
+import gen_binemit
 
 parser = argparse.ArgumentParser(description='Generate sources for Cretonne.')
 parser.add_argument('--out-dir', help='set output directory')
@@ -27,4 +28,5 @@ gen_settings.generate(isas, out_dir)
 gen_encoding.generate(isas, out_dir)
 gen_legalizer.generate(isas, out_dir)
 gen_registers.generate(isas, out_dir)
+gen_binemit.generate(isas, out_dir)
 gen_build_deps.generate()