lib/codegen-meta moved into lib/codegen. (#423)

* lib/codegen-meta moved into lib/codegen.

* Renamed codegen-meta and existing meta.

lib/codegen/meta-python/isa/__init__.py

@@ -0,0 +1,24 @@
+"""
+Cranelift target ISA definitions
+--------------------------------
+
+The :py:mod:`isa` package contains sub-packages for each target instruction set
+architecture supported by Cranelift.
+"""
+from __future__ import absolute_import
+from cdsl.isa import TargetISA  # noqa
+from . import riscv, x86, arm32, arm64
+
+try:
+    from typing import List  # noqa
+except ImportError:
+    pass
+
+
+def all_isas():
+    # type: () -> List[TargetISA]
+    """
+    Get a list of all the supported target ISAs. Each target ISA is represented
+    as a :py:class:`cranelift.TargetISA` instance.
+    """
+    return [riscv.ISA, x86.ISA, arm32.ISA, arm64.ISA]