Restore the allocator shim on Windows. Add 2Gb limit on allocations v…

…ia the shim. Remove tcmalloc from Windows.

Restore working tcmalloc_unittests on Linux and allocator_unittests on other platforms.  Add Death tests to base_unittests SecurityTests.  Fix prep_libc.py to actually strip the objects correctly.

BUG=169327,434397
TEST=base_unittests --gtest_filter=SecurityTest.*
TEST=allocator_unittests, tcmalloc_unittest

Review URL: https://codereview.chromium.org/774683003

Cr-Commit-Position: refs/heads/master@{#311194}