autoconf: Sane --enable-debug defaults.

Don't optimize at all when --enable-debug is supplied. This makes sure
that nothing is optimized out.

configure.ac

@@ -239,7 +239,7 @@ AM_CONDITIONAL(ENABLE_MAN, test "$enable_man" != no)
 # Enable debug
 AC_ARG_ENABLE([debug],
     [AS_HELP_STRING([--enable-debug],
-                    [use debug compiler flags and macros (default is no)])],
+                    [use compiler flags and macros suited for debugging (default is no)])],
     [enable_debug=$enableval],
     [enable_debug=no])
 
@@ -271,12 +271,9 @@ if test "x$enable_debug" = xyes; then
   if test "x$CXXFLAGS_overridden" = xno; then
 	CXXFLAGS=""
   fi
-  # Prefer -Og, fall back to -O0 if that is unavailable.
-  AX_CHECK_COMPILE_FLAG(
-    [-Og],
-    [[DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -Og"]],
-    [AX_CHECK_COMPILE_FLAG([-O0],[[DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -O0"]],,[[$CXXFLAG_WERROR]])],
-    [[$CXXFLAG_WERROR]])
+
+  # Disable all optimizations
+  AX_CHECK_COMPILE_FLAG([-O0], [[DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -O0"]],,[[$CXXFLAG_WERROR]])
 
   # Prefer -g3, fall back to -g if that is unavailable.
   AX_CHECK_COMPILE_FLAG(