Revert "build-sys: compile with -Og or -O1 when --enable-debug"

This reverts commit 906548689e.
Even with -Og, the debug experience is noticeably worse
because gdb shows a lot more "<optimised out>" variables and
function arguments.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -5368,19 +5368,8 @@ if test "$gcov" = "yes" ; then
   LDFLAGS="-fprofile-arcs -ftest-coverage $LDFLAGS"
 elif test "$fortify_source" = "yes" ; then
   CFLAGS="-O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 $CFLAGS"
-elif test "$debug" = "yes"; then
-  if compile_prog "-Og" ""; then
-      CFLAGS="-Og $CFLAGS"
-  elif compile_prog "-O1" ""; then
-      CFLAGS="-O1 $CFLAGS"
-  fi
-  # Workaround GCC false-positive Wuninitialized bugs with Og or O1:
-  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
-  if cc_has_warning_flag "-Wno-maybe-uninitialized"; then
-      CFLAGS="-Wno-maybe-uninitialized $CFLAGS"
-  fi
-else
-    CFLAGS="-O2 $CFLAGS"
+elif test "$debug" = "no"; then
+  CFLAGS="-O2 $CFLAGS"
 fi
 
 if test "$have_asan" = "yes"; then