[compiler-rt] Fix AllocatorCacheDeallocNewThread unittest

[etienneb]

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)

lib/sanitizer_common/tests/sanitizer_allocator_test.cc

TEST(Allocator, AllocatorCacheDeallocNewThread) {
   NewThreadParams *params = reinterpret_cast<NewThreadParams*>(
       main_cache.Allocate(&allocator, class_id));
   params->thread_cache = &child_cache;
   params->allocator = &allocator;
   params->class_id = class_id;
   pthread_t t;
   PTHREAD_CREATE(&t, 0, DeallocNewThreadWorker, params);
   PTHREAD_JOIN(t, 0);
+
+  allocator.TestOnlyUnmap();
 }
 #endif
 
 TEST(Allocator, Basic) {
   char *p = (char*)InternalAlloc(10);
   EXPECT_NE(p, (char*)0);
   char *p2 = (char*)InternalAlloc(20);
   EXPECT_NE(p2, (char*)0);