Move cygwin_dir to common.gypi.

dart/runtime/vm/vm.gypi

Index: dart/runtime/vm/vm.gypi
diff --git a/dart/runtime/vm/vm.gypi b/dart/runtime/vm/vm.gypi
index 9d91a8fe8398b9bbf3f10a3ad5d868741afbc1e9..9718a309a32146fc6c45399ec7bb8f8d1d9e5767 100644
--- a/dart/runtime/vm/vm.gypi
+++ b/dart/runtime/vm/vm.gypi
@@ -12,7 +12,6 @@
     'snapshot_test_dat_file': '<(SHARED_INTERMEDIATE_DIR)/snapshot_test.dat',
     'snapshot_test_in_dat_file': 'snapshot_test_in.dat',
     'snapshot_test_dart_file': 'snapshot_test.dart',
-    'cygwin_dir': '../../third_party/cygwin',
   },
   'targets': [
     {
@@ -91,11 +90,6 @@
     {
       'target_name': 'generate_corelib_cc_file',
       'type': 'none',
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
-        }],
-      ],
       'includes': [
         # Load the runtime implementation sources.
         '../lib/lib_sources.gypi',
@@ -136,11 +130,6 @@
     {
       'target_name': 'generate_corelib_impl_cc_file',
       'type': 'none',
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
-        }],
-      ],
       'includes': [
         # Load the runtime implementation sources.
         '../lib/lib_impl_sources.gypi',
@@ -181,11 +170,6 @@
     {
       'target_name': 'generate_mirrors_cc_file',
       'type': 'none',
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
-        }],
-      ],
       'includes': [
         # Load the shared core library sources.
         '../lib/mirrors_sources.gypi',
@@ -224,11 +208,6 @@
     {
       'target_name': 'generate_isolate_cc_file',
       'type': 'none',
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
-        }],
-      ],
       'includes': [
         # Load the runtime implementation sources.
         '../lib/isolate_sources.gypi',
@@ -267,11 +246,6 @@
     {
       'target_name': 'generate_snapshot_test_dat_file',
       'type': 'none',
-      'conditions': [
-        ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
-        }],
-      ],
       'actions': [
         {
           'action_name': 'generate_snapshot_test_dat',