Add 3.8-dev to point to `master`

Push 3.7-dev to `3.7` branch

plugins/python-build/bin/python-build

@@ -1773,6 +1773,11 @@ build_package_verify_py37() {
   build_package_verify_py36 "$1" "${2:-3.7}"
 }
 
+# Post-install check for Python 3.8.x
+build_package_verify_py38() {
+  build_package_verify_py37 "$1" "${2:-3.8}"
+}
+
 build_package_ez_setup() {
   local ez_setup="ez_setup.py"
   rm -f "${ez_setup}"

plugins/python-build/share/python-build/3.7-dev

@@ -1,4 +1,4 @@
 #require_gcc
 install_package "openssl-1.0.2k" "https://www.openssl.org/source/openssl-1.0.2k.tar.gz#6b3977c61f2aedf0f96367dcfb5c6e578cf37e7b8d913b4ecb6643c3cb88d8c0" mac_openssl --if has_broken_mac_openssl
 install_package "readline-6.3" "https://ftpmirror.gnu.org/readline/readline-6.3.tar.gz#56ba6071b9462f980c5a72ab0023893b65ba6debb4eeb475d7a563dc65cafd43" standard --if has_broken_mac_readline
-install_git "Python-3.7-dev" "https://github.com/python/cpython" master standard verify_py37 ensurepip
+install_git "Python-3.7-dev" "https://github.com/python/cpython" "3.7" standard verify_py37 ensurepip

plugins/python-build/share/python-build/3.8-dev

@@ -0,0 +1,4 @@
+#require_gcc
+install_package "openssl-1.0.2k" "https://www.openssl.org/source/openssl-1.0.2k.tar.gz#6b3977c61f2aedf0f96367dcfb5c6e578cf37e7b8d913b4ecb6643c3cb88d8c0" mac_openssl --if has_broken_mac_openssl
+install_package "readline-6.3" "https://ftpmirror.gnu.org/readline/readline-6.3.tar.gz#56ba6071b9462f980c5a72ab0023893b65ba6debb4eeb475d7a563dc65cafd43" standard --if has_broken_mac_readline
+install_git "Python-3.8-dev" "https://github.com/python/cpython" master standard verify_py38 ensurepip