python-semanage: fix cross-compilation, add test.sh

Add HOST_PYTHON3_PIP_VARS and --no-build-isolation to MAKE_VARS.
Without --no-build-isolation, pip creates an isolated build environment
which fails during cross-compilation because _sysconfigdata is missing.
Aligns with python-selinux which already has this fix.

The libsemanage pywrap uses the host Python's EXT_SUFFIX to name the
C extension, so we will use the PYCEXT env-var to correct that.

Add basic test.sh to verify the semanage Python bindings load correctly
in environments without SELinux kernel support.

Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>

lang/python/python-semanage/test.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+[ "$1" = python3-semanage ] || exit 0
+
+python3 - <<'EOF'
+import semanage
+
+# Verify the C extension loaded and key functions/constants are available
+assert hasattr(semanage, 'semanage_handle_create'), "semanage_handle_create missing"
+assert hasattr(semanage, 'SEMANAGE_CON_DIRECT'), "SEMANAGE_CON_DIRECT missing"
+assert hasattr(semanage, 'SEMANAGE_CON_INVALID'), "SEMANAGE_CON_INVALID missing"
+assert hasattr(semanage, 'SEMANAGE_FCONTEXT_ALL'), "SEMANAGE_FCONTEXT_ALL missing"
+assert hasattr(semanage, 'SEMANAGE_FCONTEXT_REG'), "SEMANAGE_FCONTEXT_REG missing"
+
+print("python3-semanage OK")
+EOF