Fix bad -pthread default when cross-compiling

See astral-sh#599.

Author: geofft

cpython-unix/build-cpython.sh

@@ -306,6 +306,12 @@ else
     patch -p1 -i "${ROOT}/patch-python-configure-add-enable-static-libpython-for-interpreter-${PYTHON_MAJMIN_VERSION}.patch"
 fi
 
+# When cross-compiling, ./configure checks that run code cannot be run,
+# and some of the defaults are wrong or unwanted, so we have to fix
+# those manually.
+# TODO(geofft): This cannot be the only thing.
+patch -p1 -i "${ROOT}/patch-python-configure-cross-assume-pthread.patch"
+
 # We patched configure.ac above. Reflect those changes.
 autoconf
 

cpython-unix/patch-python-configure-cross-assume-pthread.patch

@@ -0,0 +1,26 @@
+From c2bea55e3a2a31fc490d1a79c1dd2e413333148b Mon Sep 17 00:00:00 2001
+From: Geoffrey Thomas <[email protected]>
+Date: Tue, 6 May 2025 15:47:47 -0400
+Subject: [PATCH 1/1] configure.ac: When cross-compiling, assume -pthread works
+ (astral-sh/python-build-standalone#599)
+
+---
+ configure.ac | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/configure.ac b/configure.ac
+index a3a5ac1cdce..3134ca2c974 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -2927,7 +2927,7 @@ int main(void){
+   (void)pthread_detach(p);
+   return 0;
+ }
+-]])],[ac_cv_pthread=yes],[ac_cv_pthread=no],[ac_cv_pthread=no])
++]])],[ac_cv_pthread=yes],[ac_cv_pthread=no],[ac_cv_pthread=yes])
+ CC="$ac_save_cc"])
+ fi
+ 
+-- 
+2.39.5 (Apple Git-154)
+