Add a GYP_DEFINE to force generating /Z7 flags for Visual C++.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 73a7202fa733b342b8f503851beae13aaace5bfb..b502f405014793962cd0f393b13cdf684a0f78f4 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -631,6 +631,11 @@
     # Currently ignored on Windows.
     'coverage%': 0,
 
+    # Set to 1 to force Visual C++ to use legacy debug information format /Z7.
+    # This is useful for parallel compilation tools which can't support /Zi.
+    # Only used on Windows.
+    'z7%' : 0,

[scottmg, 2012/05/22 20:33:15]

please change to win_z7, most flags are prefixed when they only apply to one
platform.

[arthurhsu, 2012/05/22 20:37:29]

Done.

+
     # Although base/allocator lets you select a heap library via an
     # environment variable, the libcmt shim it uses sometimes gets in
     # the way.  To disable it entirely, and switch to normal msvcrt, do e.g.
@@ -1458,6 +1463,15 @@
         'include_dirs': [
           '<(DEPTH)/third_party/wtl/include',
         ],
+        'conditions': [
+          ['z7!=0', {
+            'msvs_settings': {
+              'VCCLCompilerTool': {
+                'DebugInformationFormat': '1',
+              }
+            }
+          }],
+        ],  # z7!=0
       }],  # OS==win
       ['enable_task_manager==1', {
         'defines': [