Fix lulpeg benchmark arg handling for harness compatibility

[Pavel-Durov]

luagrammar.lua expects arg[1]=module path and arg[2]=source file when run standalone, but via the harness arg contains harness arguments (arg[1]="lulpeg", arg[2]="1"), causing it to load the benchmark object instead of the LuLPeg library.

Fix by temporarily setting arg to the expected values before dofile().

[ltratt]

I can buy this. I'll tag @vext01 so he can look at this next week, but in the meantime I think this is worth merging.

[Pavel-Durov]

Without this fix I get:

RUST_BACKTRACE=full YKD_LOG=4 LUA_PATH="?.lua;../../awfy/Lua/?.lua" sh ../../../haste_harness.sh /tmp/out ~/yklua/src/lua lulpeg 1
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-tracing: stop-tracing
yk-tracing: start-tracing
yk-warning: tracing-aborted: tracing unrolled a loop
yk-tracing: start-tracing
yk-tracing: stop-tracing
Starting lulpeg benchmark ...
yk-warning: trace-compilation-aborted: Unimplemented: '%216 = insertelement <8 x i64> poison, i64 %215, i64 0'
~/yklua/src/lua: LuLPeg/tests/luagrammar.lua:7: attempt to call a nil value (field 'setmaxstack')
stack traceback:
        LuLPeg/tests/luagrammar.lua:7: in main chunk
        [C]: in function 'dofile'
        lulpeg.lua:16: in function 'lulpeg.inner_benchmark_loop'
        ../../awfy/Lua/harness.lua:48: in method 'measure'
        ../../awfy/Lua/harness.lua:59: in method 'do_runs'
        ../../awfy/Lua/harness.lua:42: in method 'run_benchmark'
        ../../awfy/Lua/harness.lua:96: in main chunk
        [C]: in ?
error: failed to run inner harness

[ltratt]

FWIW I think cd might be having a vaguely similar problem. It fails sometimes under harness.sh but survives 100s of run under try_repeat.