To get around this error which often happens in step9 build after
first 8 steps have been built:
.......RPython traceback:
File "rpython_jit_metainterp_compile.c", line 21356, in send_loop_to_backend
File "rpython_jit_backend_x86_assembler.c", line 1905, in Assembler386_assemble_loop
File "rpython_jit_backend_x86_regalloc.c", line 309, in RegAlloc_prepare_loop
File "rpython_jit_backend_x86_regalloc.c", line 978, in RegAlloc__prepare
File "rpython_jit_backend_llsupport_regalloc.c", line 6519, in compute_vars_longevity
Fatal RPython error: AssertionError
Makefile:14: recipe for target 'step9_try' failed