[msan] Do not unpoison heap if running on simulator.

With the simulator, MSan detects all memory accesses from JIT code
without the need for annotations.

We'd like to keep the annotation in the native (w/o simulator) mode
until we can move all MSan+V8 users to simulator mode.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/212833002

Patch from Evgeniy Stepanov <eugenis@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20399 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MSan does not understand inline asm. This change preinitializes cpuid
results, and disables the use of stos.

Random mmap() addresses conflict with sanitizer memory layout.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/212723003

Patch from Evgeniy Stepanov <eugenis@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20400 ce2b1a6d-e550-0410-aec6-3dcde31c8c00