python_pep517: move PEP517_SOURCE_PATH to python_pep517

Now we have the start of a PEP-517 base class, the PEP517_SOURCE_PATH
variable can be defined in there instead of the classes that use it.

(From OE-Core rev: 69944121f49f613568bf0c62ae6b3b47af195dbe)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/flit_core.bbclass

@@ -6,9 +6,6 @@ flit_core_do_configure () {
     :
 }
 
-# Where to execute the build process from
-PEP517_SOURCE_PATH ?= "${S}"
-
 # TODO: ideally this uses pypa/build
 flit_core_do_compile () {
     cd ${PEP517_SOURCE_PATH}

meta/classes/python_pep517.bbclass

@@ -3,6 +3,9 @@
 
 DEPENDS:append = " python3-pip-native"
 
+# Where to execute the build process from
+PEP517_SOURCE_PATH ?= "${S}"
+
 # The directory where wheels should be written too. Build classes
 # will ideally [cleandirs] this but we don't do that here in case
 # a recipe wants to install prebuilt wheels.

meta/classes/setuptools_build_meta.bbclass

@@ -2,9 +2,6 @@ inherit setuptools3-base python_pep517
 
 DEPENDS += "python3-setuptools-native python3-wheel-native"
 
-# Where to execute the build process from
-PEP517_SOURCE_PATH ?= "${S}"
-
 setuptools_build_meta_do_configure () {
     :
 }