python3-pip: Fix error when installing packages that require compilation

This addresses one of the issues raised in #11912.

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

lang/python/python3-version.mk

@@ -13,7 +13,7 @@ PYTHON3_VERSION_MICRO:=2
 PYTHON3_VERSION:=$(PYTHON3_VERSION_MAJOR).$(PYTHON3_VERSION_MINOR)
 
 PYTHON3_SETUPTOOLS_PKG_RELEASE:=1
-PYTHON3_PIP_PKG_RELEASE:=2
+PYTHON3_PIP_PKG_RELEASE:=3
 
 PYTHON3_SETUPTOOLS_VERSION:=41.2.0
 PYTHON3_PIP_VERSION:=19.2.3

lang/python/python3/patches-pip/001-pep517-pyc-fix.patch

@@ -0,0 +1,13 @@
+diff -Nurp a/pip/_vendor/pep517/wrappers.py b/pip/_vendor/pep517/wrappers.py
+--- a/pip/_vendor/pep517/wrappers.py	2019-07-30 20:02:13.000000000 +0800
++++ b/pip/_vendor/pep517/wrappers.py	2020-04-24 17:23:35.764905235 +0800
+@@ -10,6 +10,9 @@ from . import compat
+ 
+ _in_proc_script = pjoin(dirname(abspath(__file__)), '_in_process.py')
+ 
++if not os.path.isfile(_in_proc_script):
++    _in_proc_script = pjoin(dirname(abspath(__file__)), '_in_process.pyc')
++
+ 
+ @contextmanager
+ def tempdir():