unix: backport a libffi aarch64 assembly fix

LLVM 19 yields a compile error without this patch.

Author: indygreg

cpython-unix/build-libffi.sh

@@ -13,6 +13,43 @@ tar -xf libffi-${LIBFFI_VERSION}.tar.gz
 
 pushd libffi-${LIBFFI_VERSION}
 
+# Needed to fix compilation on macOS aarch64. Will presumably be in libffi
+# 3.4.7 or 3.5. Backport of libffi commit 8308bed5b2423878aa20d7884a99cf2e30b8daf7.
+patch -p1 <<EOF
+diff --git a/src/aarch64/sysv.S b/src/aarch64/sysv.S
+index fdd0e8b..1ae768b 100644
+--- a/src/aarch64/sysv.S
++++ b/src/aarch64/sysv.S
+@@ -89,7 +89,6 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+    x5 closure
+ */
+
+-	cfi_startproc
+ CNAME(ffi_call_SYSV):
+ 	BTI_C
+ 	/* Sign the lr with x1 since that is where it will be stored */
+@@ -347,8 +346,8 @@ CNAME(ffi_closure_SYSV_V):
+ #endif
+
+ 	.align	4
+-	cfi_startproc
+ CNAME(ffi_closure_SYSV):
++	cfi_startproc
+ 	BTI_C
+ 	SIGN_LR
+ 	stp     x29, x30, [sp, #-ffi_closure_SYSV_FS]!
+@@ -643,8 +642,8 @@ CNAME(ffi_go_closure_SYSV_V):
+ #endif
+
+ 	.align	4
+-	cfi_startproc
+ CNAME(ffi_go_closure_SYSV):
++	cfi_startproc
+ 	BTI_C
+ 	stp     x29, x30, [sp, #-ffi_closure_SYSV_FS]!
+ 	cfi_adjust_cfa_offset (ffi_closure_SYSV_FS)
+EOF
+
 EXTRA_CONFIGURE=
 
 # mkostemp() was introduced in macOS 10.10 and libffi doesn't have