Compile top level while loops in JIT. * src/pt-eval.cc (tree_evaluator::visit_while_command): Try compile while loops. * src/pt-jit.cc (jit_convert::jit_convert): Add first terminator to worklist. (tree_jit::execute): New overload. * src/pt-jit.h (tree_jit::execute): New overload. * src/pt-loop.cc (tree_while_command::~tree_while_command): Delete compiled. (tree_simple_for_command::~tree_simple_for_command): Only delete compiled if JIT is enabled. * src/pt-loop.h (tree_while_command::get_info, tree_while_command::stash_info): New function.