Make the debug build compile with -Og

Due to Python's handling of CFLAGS and the way we
were passing extra compiler flags through the SPEC
the -Og flag for the debug build was overridden by
the -O2 flag, resulting in various side effects.

See: https://bugs.python.org/issue37631

Resolves: rhbz#1678277

python38.spec

@@ -690,7 +690,7 @@ BuildPython() {
 
 
   # Invoke the build
-  %make_build EXTRA_CFLAGS="$CFLAGS $MoreCFlags"
+  %make_build CFLAGS_NODIST="$CFLAGS_NODIST $MoreCFlags"
 
   popd
   echo FINISHED: BUILD OF PYTHON FOR CONFIGURATION: $ConfName