[compiler-rt] Fix AllocatorCacheDeallocNewThread unittest

Summary:
The unittest was not freeing the mapped memory.


```
Repeating all tests (iteration 1) . . .

Note: Google Test filter = Allocator.AllocatorCacheDeallocNewThread
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from Allocator
[ RUN      ] Allocator.AllocatorCacheDeallocNewThread
[       OK ] Allocator.AllocatorCacheDeallocNewThread (3 ms)
[----------] 1 test from Allocator (4 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (5 ms total)
[  PASSED  ] 1 test.

Repeating all tests (iteration 2) . . .

Note: Google Test filter = Allocator.AllocatorCacheDeallocNewThread
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from Allocator
[ RUN      ] Allocator.AllocatorCacheDeallocNewThread
==4504==WARNING: SanitizerTool failed to mprotect 0x010000003000 (1099511640064) bytes at 0x010000000000 (error code: 48
7)
==4504==Sanitizer CHECK failed: D:/src/llvm/llvm/projects/compiler-rt/lib\sanitizer_common/sanitizer_allocator.h:329 ((kSpaceBeg)) == ((reinterpret_cast<uptr>( MmapFixedNoAccess(kSpaceBeg, TotalSpaceSize)))) (1099511627776, 0)
```

Reviewers: rnk

Subscribers: llvm-commits, kubabrecka, chrisha

Differential Revision: http://reviews.llvm.org/D22094

llvm-svn: 274764