This patch adds basic memory sanitizer support for loongarch64
with 47-bit VMA, which memory layout is based on x86_64.
The LLVM part of the LoongArch memory sanitizer implementation will
be done separately, which will fix failing tests in check-msan.
These failing tests fail with the following same error: "error in
backend: unsupported architecture".
Reviewed By: #sanitizers, vitalybuka, MaskRay
Differential Revision: https://reviews.llvm.org/D140528
