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