[ASan] Enhance libsanitizer support for invalid-pointer-pair.

Following patch adds support of all memory origins in
CheckForInvalidPointerPair function. For small difference of pointers,
it's directly done in shadow memory (the limit was set to 2048B).
Then we search for origin of first pointer and verify that the second
one has the same origin. If so, we verify that it points either to a same
variable (in case of stack memory or a global variable), or to a same
heap segment.

Committing on behanf of marxin and jakubjelinek.

Reviewers: alekseyshl, kcc

Subscribers: llvm-commits

Differential revision: https://reviews.llvm.org/D40600

llvm-svn: 319668