exec: fix div instruction

[laizy]

spec ref: https://webassembly.github.io/spec/core/exec/numerics.html#op-idiv-s

this fix passed the testcase in https://github.com/WebAssembly/testsuite/blob/master/i32.wast#L64

[codecov-io]

Codecov Report

Merging #186 into master will decrease coverage by 0.73%. The diff coverage is 40.74%.

@@            Coverage Diff             @@
##           master     #186      +/-   ##
==========================================
- Coverage   69.77%   69.03%   -0.74%     
==========================================
  Files          49       51       +2     
  Lines        5495     5910     +415     
==========================================
+ Hits         3834     4080     +246     
- Misses       1318     1467     +149     
- Partials      343      363      +20

Impacted Files	Coverage Δ
exec/vm.go	80.13% <0%> (-3.14%)	:arrow_down:
wasm/module.go	72.88% <100%> (ø)	:arrow_up:
wasm/types.go	46.15% <100%> (+0.32%)	:arrow_up:
wasm/index.go	58.55% <33.33%> (-3.32%)	:arrow_down:
exec/call.go	76.92% <50%> (-5.69%)	:arrow_down:
exec/num.go	98.67% <60%> (-1.33%)	:arrow_down:
exec/memory.go	84.42% <66.66%> (-1.9%)	:arrow_down:
wast/write.go	70.15% <0%> (ø)	:arrow_up:
wast/scanner.go	55.64% <0%> (ø)
wast/token.go	65% <0%> (ø)
... and 1 more

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[laizy]

@sbinet ,review?

[laizy]

No rush to merge. we have build a test runner for the spec testsuite in our forked repo, and found some other issues. We will submit the fixes with the test runner code soon.

[sbinet]

ping?

[laizy]

@sbinet sorry for late reply. Have appended commits for test runner and some bug fix.