Revert "Error out on invalid LLDB build configurations on OS X."

This reverts commit b08610b.

The check for LLDB build variant really needs to happen in
build-script-impl.  build-script can still take options after
the '--' separator that may control the final determination
of the LLDB build variant.  These weren't all being considered
by the logic in build-script.

Author: Todd Fiala

Diff for: utils/build-script

@@ -604,27 +604,6 @@ placed""",
         build_script_impl_inferred_args += [
             "--skip-build-lldb"
         ]
-    else:
-        import platform
-        if platform.system() == "Darwin":
-            # Validate the LLDB build variant, exiting the
-            # build if it is not supported.
-            supported_variants = [
-                "Debug",
-                "Release"
-                ]
-            if args.lldb_build_variant is not None:
-                lldb_build_variant = args.lldb_build_variant
-            else:
-                lldb_build_variant = args.build_variant
-            if lldb_build_variant not in supported_variants:
-                sys.stderr.write(
-                    "The Swift LLDB build does not support build variant %s\n"
-                    % lldb_build_variant)
-                sys.stderr.write(
-                    "Please select one of the following variants: %s\n" %
-                    ", ".join(supported_variants))
-                sys.exit(1)
 
     if not args.build_llbuild:
         build_script_impl_inferred_args += [