Use abstract configurations to switch between opt debug settings

The problem is that conditions are evaluated before configuration inheritance is resolved, so we can't just define a configuration like this:

'Optdebug': {
  'inherits_from': ['Debug'],
  'variables': {
    'v8_optimized_debug': 2,
  }
}

Instead, we have to put the different settings depending on the optimization level into separate configurations, and use conditions inside the concrete configurations to inherit from the correct base class.

Common settings go in the base configuration DebugBaseCommon, and v8_optimized_debug dependent settings go into DebugBase{0,1,2}

The new Debug configuration inherits from DebugBaseCommon and DebugBase<(v8_optimized_debug), while the new configuration Optdebug inherits from DebugBaseCommon and DebugBase2.

BUG=v8:3252
R=machenbach@chromium.org, jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/224443003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20605 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/features.gypi

@@ -98,7 +98,8 @@
       }],
     ],  # conditions
     'configurations': {
-      'Debug': {
+      'DebugBaseCommon': {
+        'abstract': 1,
         'variables': {
           'v8_enable_extra_checks%': 1,
           'v8_enable_handle_zapping%': 1,

build/standalone.gypi

@@ -135,9 +135,15 @@
     },
     'default_configuration': 'Debug',
     'configurations': {
-      'Debug': {
+      'DebugBaseCommon': {
         'cflags': [ '-g', '-O0' ],
       },
+      'Optdebug': {
+        'inherit_from': [ 'DebugBaseCommon', 'DebugBase2' ],
+      },
+      'Debug': {
+        # Xcode insists on this empty entry.
+      },
       'Release': {
         # Xcode insists on this empty entry.
       },