Update spkg-build.in to set PKG_CONFIG_PATH and CPPFLAGS for Python 3.13+ compatibility

Author: cxzhong

build/pkgs/python3/spkg-build.in

@@ -62,6 +62,19 @@ export EXTRA_CFLAGS="`testcflags.sh -Wno-unused $OLD_CFLAGS`"
     # https://github.com/sagemath/sage/issues/23398
     PYTHON_CONFIGURE="$PYTHON_CONFIGURE --without-ensurepip"
 
+# Set PKG_CONFIG_PATH to help Python 3.13+ find sqlite3 and other dependencies
+# Python 3.13 changed its build system and now uses pkg-config at configure time
+if [ -n "$SAGE_LOCAL" ]; then
+    export PKG_CONFIG_PATH="$SAGE_LOCAL/lib/pkgconfig:${PKG_CONFIG_PATH}"
+fi
+
+# Ensure Python can find headers and libraries during configure (not just make)
+# This is critical for Python 3.13+ which detects extension modules at configure time
+if [ -n "$SAGE_LOCAL" ]; then
+    export CPPFLAGS="-I$SAGE_LOCAL/include $CPPFLAGS"
+    export LDFLAGS="-L$SAGE_LOCAL/lib $LDFLAGS"
+fi
+
 sdh_configure --enable-shared $PYTHON_CONFIGURE
 
 # Make sure -L. is placed before -L$SAGE_LOCAL/lib so that python and extension