On Windows builds, not all private symbols are exported.

make/windows/build_vm_def.sh generates vm.def file for the list of function symbols to be exported. It appears to only pick symbols with signature "??_7.*@@6B@", which, according to this wiki (http://en.wikipedia.org/wiki/Microsoft_Visual_C%2B%2B_Name_Mangling#Encoded_Number), they are 'vftable's functions, the rest symbols are not exported.

Missing symbols will result inaccurate callsite.
The logic is dated back to 1.5.