https://github.com/llvm/llvm-project/issues/139561

Fixes #122367

FreeListHeap uses the _end symbol which conflicts with the _end symbol
defined by GPU start.cpp files so for now we exclude the test and the
fuzzer on GPU.

This better matches the structure we use for the rest of libc.

This reverts commit 93b83642ee34d0092b94776728dad0117c2b72a1.

 - Correct riscv32 assumption about alignment (bit of a hack).
 - Fix test case where the largest_small and smallest sizes are the
   same.

This reverts commit b05600d96f46697e21f6b1b7ad901391326243a8.
riscv32 unit test still broken

 - Fix assertion expressions.
 - Fix incorrect small size in freestore_test.
 - There may only be one small size for high alignment and small
   pointers (riscv32).
 - Don't rely on stack alignment in FreeList test.

Reverts llvm/llvm-project#106259

Unit tests break on AArch64.

This reworks the free store implementation in libc's malloc to use a
dlmalloc-style binary trie of circularly linked FIFO free lists. This
data structure can be maintained in logarithmic time, but it still
permits a relatively small implementation compared to other
logarithmic-time ordered maps.

The implementation doesn't do the various bitwise tricks or
optimizations used in actual dlmalloc; it instead optimizes for
(relative) readability and minimum code size. Specific optimization can
be added as necessary given future profiling.