[msan] Mprotect all inaccessible memory regions.

Fix 2 bugs in memory mapping setup:
- the invalid region at offset 0 was not protected because mmap at
  address 0 fails with EPERM on most Linux systems. We did not
  notice this because the check condition was flipped: the code was
  checking that mprotect has failed. And the test that was supposed
  to catch this was weakened by the mitigations in the mmap
  interceptor.
- when running without origins, the origin shadow range was left
  unprotected.

The new test ensures that mmap w/o MAP_FIXED always returns valid
application addresses.

llvm-svn: 238109