python,python3: Include python-config for target Python in InstallDev

This installs python{2.7,3.7}-config in $(STAGING_DIR)/usr/bin as part
of Build/InstallDev, to be used by other packages to get build
configuration for target Python.

The treatment for Python 2 and 3 are a bit different:

* For Python 2, python-config is a Python script that is expected to be
  run with, and return data for, the installed Python interpreter. This
  installs a modified version of this script, to be run using host
  Python, and read/return data for target Python.

* Python 3 includes a shell script version of python-config (expected to
  be used in cross-compilation scenarios). This simply installs the
  script into the right place.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

lang/python/python/Makefile

@@ -12,7 +12,7 @@ include ../python-version.mk
 
 PKG_NAME:=python
 PKG_VERSION:=$(PYTHON_VERSION).$(PYTHON_VERSION_MICRO)
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE:=Python-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://www.python.org/ftp/python/$(PKG_VERSION)
@@ -195,6 +195,8 @@ endef
 
 define Build/InstallDev
 	$(INSTALL_DIR) $(1)/usr/include $(1)/usr/lib $(1)/usr/lib/pkgconfig
+	$(INSTALL_DIR) $(1)/usr/bin
+	$(INSTALL_DIR) $(1)/usr/lib/python$(PYTHON_VERSION)-openwrt
 	$(CP) \
 		$(PKG_INSTALL_DIR)/usr/include/python$(PYTHON_VERSION) \
 		$(1)/usr/include/
@@ -205,6 +207,15 @@ define Build/InstallDev
 	$(CP) \
 		$(PKG_INSTALL_DIR)/usr/lib/pkgconfig/python*.pc \
 		$(1)/usr/lib/pkgconfig
+	$(INSTALL_BIN) \
+		./files/python-config.in \
+		$(1)/usr/bin/python$(PYTHON_VERSION)-config
+	$(SED) \
+		's|@EXENAME@|$(HOST_PYTHON_DIR)/bin/python$(PYTHON_VERSION)|' \
+		$(1)/usr/bin/python$(PYTHON_VERSION)-config
+	$(CP) \
+		$(PKG_INSTALL_DIR)/usr/lib/python$(PYTHON_VERSION)/_sysconfigdata.py \
+		$(1)/usr/lib/python$(PYTHON_VERSION)-openwrt/_sysconfigdatatarget.py
 endef
 
 PYTHON_BASE_LIB_FILES:= \