Defer acquiring the FDE lock until after the allocation. This can avoid
nesting issues between malloc and backtrace when using LSan.

Avoid negative shift.

Fix binary search when search value is in the last block, but not equal
to the start of the range. PR 49444.

Fix braino in last commit and free the node iff the insert failed.

Use static_cast for rb_tree_insert_node void * return value.

GC unwind_info_size.

SH3 uses unaligned data in the .eh_frame section, so use memcpy.

Pass down data_base just in case something actually tries to use it.

Add more const to make GCC happy.

Add a heavily modified version of Apple's libunwind as released under
MIT license in libc++abi. At the moment, only x86 support is tested.