Tweak optimization for Windows MSYS builds

Too many symbols to do completely unoptimized builds on Windows, so -Og
is necessary.

libs/ardour/wscript

@@ -1,6 +1,8 @@
 #!/usr/bin/env python
 from waflib.extras import autowaf as autowaf
 from waflib import Options, Task
+import sys
+import platform as PLATFORM
 import os
 import re
 
@@ -384,6 +386,7 @@ def build(bld):
     # Library
     if bld.is_defined ('INTERNAL_SHARED_LIBS'):
         obj              = bld.shlib(features = 'c cxx cshlib cxxshlib', source=sources)
+        obj.cxxflags     = []
         # macros for this shared library
         obj.defines      = [ 'LIBARDOUR_DLL_EXPORTS=1' ]
     else:
@@ -410,6 +413,9 @@ def build(bld):
                         ]
     if bld.env['build_target'] != 'mingw':
         obj.uselib += ['DL']
+    elif sys.platform == "win32":
+        obj.cxxflags += ['-Og']
+
 
     if bld.is_defined('USE_EXTERNAL_LIBS'):
         obj.uselib.extend(['VAMPSDK', 'LIBLTC', 'LIBFLUIDSYNTH'])