move conditions using 'component' to 'target_defaults'

'component' was defined within NW.js building procedure. However it
wasn't defined until including 'common.gypi' when building addons.
Conditions within 'variables' cannot use variable within the same
level. Moving conditions to 'target_defaults' will make 'component'
defined before evaluating the conditions, to prevent addon building
failures.

fixed nwjs/nw-gyp#96

Author: Cong Liu

common.gypi

@@ -33,15 +33,6 @@
 
 
     'conditions': [
-      ['OS=="win" and component=="shared_library"', {
-        # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
-        'win_release_RuntimeLibrary%': '2', # 2 = /MD (nondebug DLL)
-        'win_debug_RuntimeLibrary%': '3',   # 3 = /MDd (debug DLL)
-      }, {
-        # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
-        'win_release_RuntimeLibrary%': '0', # 0 = /MT (nondebug static)
-        'win_debug_RuntimeLibrary%': '1',   # 1 = /MTd (debug static)
-      }],
       ['OS == "win"', {
         'os_posix': 0,
         'v8_postmortem_support%': 'false',
@@ -71,6 +62,19 @@
 
   'target_defaults': {
     'default_configuration': 'Release',
+    'variables': {
+      'conditions': [
+        ['OS=="win" and component=="shared_library"', {
+          # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
+          'win_release_RuntimeLibrary%': '2', # 2 = /MD (nondebug DLL)
+          'win_debug_RuntimeLibrary%': '3',   # 3 = /MDd (debug DLL)
+        }, {
+          # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
+          'win_release_RuntimeLibrary%': '0', # 0 = /MT (nondebug static)
+          'win_debug_RuntimeLibrary%': '1',   # 1 = /MTd (debug static)
+        }],
+      ],
+    },
     'configurations': {
       'Debug': {
         'variables': {