libffi: add patch to fix build error with NDK r26

Fixes #16.

patches/libffi-forward-declare-open_temp_exec_file.patch

@@ -0,0 +1,42 @@
+From cbfb9b436ab13e4b4aba867d061e11d7f89a351c Mon Sep 17 00:00:00 2001
+From: serge-sans-paille <sguelton@mozilla.com>
+Date: Wed, 1 Feb 2023 18:09:25 +0100
+Subject: [PATCH] Forward declare open_temp_exec_file
+
+It's defined in closures.c and used in tramp.c.
+Also declare it as an hidden symbol, as it should be.
+---
+ include/ffi_common.h | 4 ++++
+ src/tramp.c          | 4 ++++
+ 2 files changed, 8 insertions(+)
+
+diff --git a/include/ffi_common.h b/include/ffi_common.h
+index 2bd31b03d..c53a79493 100644
+--- a/include/ffi_common.h
++++ b/include/ffi_common.h
+@@ -128,6 +128,10 @@ void *ffi_data_to_code_pointer (void *data) FFI_HIDDEN;
+    static trampoline. */
+ int ffi_tramp_is_present (void *closure) FFI_HIDDEN;
+
++/* Return a file descriptor of a temporary zero-sized file in a
++   writable and executable filesystem. */
++int open_temp_exec_file(void) FFI_HIDDEN;
++
+ /* Extended cif, used in callback from assembly routine */
+ typedef struct
+ {
+diff --git a/src/tramp.c b/src/tramp.c
+index b9d273a1a..c3f4c9933 100644
+--- a/src/tramp.c
++++ b/src/tramp.c
+@@ -39,6 +39,10 @@
+ #ifdef __linux__
+ #define _GNU_SOURCE 1
+ #endif
++
++#include <ffi.h>
++#include <ffi_common.h>
++
+ #include <stdio.h>
+ #include <unistd.h>
+ #include <stdlib.h>