wxPython4: fix cross build after python3-module change

In build-helper 'python3', we've set _PYTHON_SYSCONFIGDATA_NAME
on cross-build, but that module could be found only inside sysroot.

srcpkgs/wxPython4/patches/cross.patch

@@ -0,0 +1,12 @@
+Index: wxPython-4.0.7/build.py
+===================================================================
+--- wxPython-4.0.7.orig/build.py
++++ wxPython-4.0.7/build.py
+@@ -169,7 +169,6 @@ def main(args):
+     setPythonVersion(args)
+     setDevModeOptions(args)
+ 
+-    os.environ['PYTHONPATH'] = phoenixDir()
+     os.environ['PYTHONUNBUFFERED'] = 'yes'
+     os.environ['WXWIN'] = wxDir()
+ 

srcpkgs/wxPython4/template

@@ -31,6 +31,7 @@ post_extract() {
 
 pre_build() {
 	chmod -R go+rX $wrksrc
+	PYTHONPATH="${PYTHONPATH:+${PYTHONPATH}:}$wrksrc"
 	if [ "$CROSS_BUILD" ]; then
 		PYPREFIX="$XBPS_CROSS_BASE"
 		LDFLAGS+=" -L${XBPS_CROSS_BASE}/${py3_lib} -L${XBPS_CROSS_BASE}/usr/lib"