Revert "Revert "configure: Switch debug build from -O0 to -Og""

This reverts commit 7dadd38161.

The latest revert cited debuggability trumping performance, but the
performance loss is su huge here that debug builds are unusable and
next promotions time out.

In the interest of progress, pick the lesser of two evils.

configure.py

@@ -286,8 +286,7 @@ modes = {
         'cxx_ld_flags': '',
         'stack-usage-threshold': 1024*40,
         # -fasan -Og breaks some coroutines on aarch64, use -O0 instead
-        # also, -Og was seen to make all variables "optimized out"
-        'optimization-level': '0',
+        'optimization-level': ('0' if platform.machine() == 'aarch64' else 'g'),
         'per_src_extra_cxxflags': {},
         'cmake_build_type': 'Debug',
         'can_have_debug_info': True,