tsan: fix mmap_lots test

[dvyukov]

Summary

If tsan runtime will try to allocate something during exit handling,
the allocation will fail because there is no VA whatsoever.
It's observed to fail with the following error in some cases:
failed to allocate 0x1000 (4096) bytes of DTLS_NextBlock.
So terminate the process immediately.

[alexfh]

LG. Thanks for the fix!

[dvyukov]

Committed in https://github.com/llvm/llvm-project/commit/fb19400d4e4c421ce61907bf92a92be8d937e584

compiler-rt/test/tsan/mmap_lots.cpp

for (size_t mmap_size = 64ull << 30; mmap_size >= 4 << 10; mmap_size /= 2) {
     size_t allocated = 0;
     while (mmap(0, mmap_size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE,
                 fd, 0) != MAP_FAILED) {
       allocated += mmap_size;
     }
     fprintf(stderr, "allocated %zu with size %zu\n", allocated, mmap_size);
   }
   fprintf(stderr, "DONE\n");
+  // If tsan runtime will try to allocate something during exit handling,
+  // the allocation will fail because there is no VA whatsoever.
+  // It's observed to fail with the following error in some cases:
+  // failed to allocate 0x1000 (4096) bytes of DTLS_NextBlock.
+  // So terminate the process immediately.
+  _exit(0);
 }
 
 // CHECK: DONE