python,python3: define PyBuild/Compile & Py3Build/Compile

Similar to LEDE/OpenWrt's Build/Compile/Default rule,
and other similarities like this.

This should allow Python packages to define
PyBuild/Compile rules to do specific stuff per
package.

The advantage of using these (over just overriding
Build/Compile) is the VARIANT mechanism that is
in place to support packaging both for Python & Python3.

So, PyBuild/Compile will get picked up for the Python
variant build, and Py3Build/Compile will get picked
up for the Python3 variant build.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

lang/python/python/files/python-package.mk

@@ -132,8 +132,10 @@ define PyBuild/Compile/Default
 	)
 endef
 
+PyBuild/Compile=$(PyBuild/Compile/Default)
+
 ifeq ($(BUILD_VARIANT),python)
 define Build/Compile
-	$(call PyBuild/Compile/Default)
+	$(call PyBuild/Compile)
 endef
 endif # python

lang/python/python3/files/python3-package.mk

@@ -132,8 +132,10 @@ define Py3Build/Compile/Default
 	)
 endef
 
+Py3Build/Compile=$(Py3Build/Compile/Default)
+
 ifeq ($(BUILD_VARIANT),python3)
 define Build/Compile
-	$(call Py3Build/Compile/Default)
+	$(call Py3Build/Compile)
 endef
 endif # python3