Bug [3601804]: platformCPUID segmentation fault on Darwin
Protect Tcl_GetIndexFromObjStruct from invalid "offset" values, like 0 or -1. Undocumented, because I don't want to promote people start using that.
Silence some compiler warnings.
revert [273bbe926d]:  it doesn't work on i386
new version of cpuid, which doesn't use the edi register any more. Hopefully that works better on some Darwin.
merge core-8-4-branch