[HWASan] Introduce non-zero based and dynamic shadow memory (compiler-rt).

Retire the fixed shadow memory mapping to avoid conflicts with default
process memory mapping (currently manifests on Android).

Tests on AArch64 show <1% performance loss and code size increase,
making it possible to use dynamic shadow memory by default.

Keep the fixed shadow memory mapping around to be able to run
performance comparison tests later.

Re-commiting D45847 with fixed shadow for x86-64.

llvm-svn: 330624