Attempt to set multiarch to a constant instead of disabling

cpython-unix/build-cpython.sh

@@ -120,7 +120,7 @@ if [ "${CC}" = "clang" ]; then
 elif [ "${CC}" = "musl-clang" ]; then
   # This appears to also be a problem for musl builds on 3.13.
   if [ -n "${PYTHON_MEETS_MINIMUM_VERSION_3_13}" ]; then
-    patch -p1 -i ${ROOT}/patch-disable-multiarch-13.patch
+    patch -p1 -i ${ROOT}/patch-musl-multiarch-13.patch
   fi
 fi
 

cpython-unix/build.py

@@ -436,6 +436,7 @@ def build_cpython_host(
             "build-cpython-host.sh",
             "patch-disable-multiarch.patch",
             "patch-disable-multiarch-13.patch",
+            "patch-musl-multiarch-13.patch",
             "patch-disable-multiarch-legacy.patch",
         }
         for s in sorted(support):

cpython-unix/patch-musl-multiarch-13.patch

@@ -0,0 +1,17 @@
+diff -u 13-a/configure.ac 13-b/configure.ac
+--- 13-a/configure.ac	2024-05-08 05:21:00.000000000 -0400
++++ 13-b/configure.ac	2024-05-19 07:42:23.294762624 -0400
+@@ -1090,12 +1090,7 @@
+ dnl architecture. PLATFORM_TRIPLET will be a pair or single value for these
+ dnl platforms.
+ AC_MSG_CHECKING([for multiarch])
+-AS_CASE([$ac_sys_system],
+-  [Darwin*], [MULTIARCH=""],
+-  [iOS], [MULTIARCH=""],
+-  [FreeBSD*], [MULTIARCH=""],
+-  [MULTIARCH=$($CC --print-multiarch 2>/dev/null)]
+-)
++MULTIARCH=x86_64-linux-musl
+ AC_SUBST([MULTIARCH])
+
+ if test x$PLATFORM_TRIPLET != x && test x$MULTIARCH != x; then