CLASSES: unexport _PYTHON_SYSCONFIGDATA_NAME to allow devtool

On Ubuntu 20.04, devtool cannot be used in recipe inheriting
python3native. Unexport _PYTHON_SYSCONFIGDATA_NAME as a workaround.
To check if it can be revert with next bitbake releases.

Signed-off-by: Lionel VITTE <lionel.vitte@st.com>
Change-Id: I7d73d05e1a5d58dedf69b3aefb3e07c35b92800d

classes/python3native.bbclass

@@ -0,0 +1,32 @@
+inherit python3-dir
+
+PYTHON="${STAGING_BINDIR_NATIVE}/python3-native/python3"
+EXTRANATIVEPATH += "python3-native"
+DEPENDS_append = " python3-native "
+
+# python-config and other scripts are using distutils modules
+# which we patch to access these variables
+export STAGING_INCDIR
+export STAGING_LIBDIR
+
+# Packages can use
+# find_package(PythonInterp REQUIRED)
+# find_package(PythonLibs REQUIRED)
+# which ends up using libs/includes from build host
+# Therefore pre-empt that effort
+export PYTHON_LIBRARY="${STAGING_LIBDIR}/lib${PYTHON_DIR}${PYTHON_ABI}.so"
+export PYTHON_INCLUDE_DIR="${STAGING_INCDIR}/${PYTHON_DIR}${PYTHON_ABI}"
+
+export _PYTHON_SYSCONFIGDATA_NAME="_sysconfigdata"
+# Unset these to stop python trying to report the target Python setup
+python () {
+    if bb.data.inherits_class('devtool-source', d):
+        bb.warn("_PYTHON_SYSCONFIGDATA_NAME unexported for devtool to fix an issue with Python on Ubuntu 20.04. Should be fixed in later version of bitbake")
+        d.setVarFlag('_PYTHON_SYSCONFIGDATA_NAME', 'unexport', '1')
+}
+
+# suppress host user's site-packages dirs.
+export PYTHONNOUSERSITE = "1"
+
+# autoconf macros will use their internal default preference otherwise
+export PYTHON