Add CPython 3.9.0a4

plugins/python-build/share/python-build/3.9.0a4

@@ -0,0 +1,10 @@
+#require_gcc
+prefer_openssl11
+export PYTHON_BUILD_CONFIGURE_WITH_OPENSSL=1
+install_package "openssl-1.1.0j" "https://www.openssl.org/source/openssl-1.1.0j.tar.gz#31bec6c203ce1a8e93d5994f4ed304c63ccf07676118b6634edded12ad1b3246" mac_openssl --if has_broken_mac_openssl
+install_package "readline-8.0" "https://ftpmirror.gnu.org/readline/readline-8.0.tar.gz#e339f51971478d369f8a053a330a190781acb9864cf4c541060f12078948e461" mac_readline --if has_broken_mac_readline
+if has_tar_xz_support; then
+  install_package "Python-3.9.0a4" "https://www.python.org/ftp/python/3.9.0/Python-3.9.0a4.tar.xz#7f976528015268ea95bf5d3f9dbeede6a1113638fe2111239afd47802907fe63" ldflags_dirs standard verify_py38 copy_python_gdb ensurepip
+else
+  install_package "Python-3.9.0a4" "https://www.python.org/ftp/python/3.9.0/Python-3.9.0a4.tgz#10549eed04d514fc2eaacfe9dbabcb814b08a0d40780948f4b7d77a643bfd055" ldflags_dirs standard verify_py38 copy_python_gdb ensurepip
+fi