Introduce new type for inteceptors UINTMAX_T

Summary:
The UINTMAX_T type will be used in new interceptors.

While there, correct the type of strtoumax(3) from INTMAX_T to UINTMAX_T.

Original patch from Yang Zheng.

Reviewers: vitalybuka, kcc, joerg

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, tomsun.0.7, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D51106

llvm-svn: 340907