The "libffi" directory holds a copy of libffi version 3.4.6.
The libffi code is distributed under an LGPL-compatible license.

Changes to the source in this copy:

 * Commented out `__attribute__((deprecated))` for `ffi_java_...` in
   "ffi.h.in" to avoid warnings when compiling libffi itself

 * Added $CPPFLAGS to use of $CC in "configure.host"

 * Disabled FFI_EXEC_TRAMPOLINE_TABLE for Mac OS AArch64 in
   "configure.ac", since we use pthread_jit_write_protect_np() in the
   Racket wrapper

 * Disabled AX_ENABLE_BUILDDIR in "configure.ac"

 * Repaired 32-bit x86 Darwin struct return for sizes 1, 2, 4, and 8

 * AArch64 CFI adjustments to comile with newer Clang, based on
   eafab2356e8dcf5f01d2bcfa311cafba3b395a7e
