[GN]: Precompiled header support for GCC.

tools/gn/variables.h

Index: tools/gn/variables.h
diff --git a/tools/gn/variables.h b/tools/gn/variables.h
index 4d8c4b4c297aa6d4bd3279bd69799c3541bf86b7..65d57a8ef3f2bb83d211480e5ca9c28cc1f4c90b 100644
--- a/tools/gn/variables.h
+++ b/tools/gn/variables.h
@@ -103,6 +103,22 @@ extern const char kCflagsObjCC[];
 extern const char kCflagsObjCC_HelpShort[];
 extern const char* kCflagsObjCC_Help;
 
+extern const char kCflagsPCHC[];
+extern const char kCflagsPCHC_HelpShort[];
+extern const char* kCflagsPCHC_Help;
+
+extern const char kCflagsPCHCC[];
+extern const char kCflagsPCHCC_HelpShort[];
+extern const char* kCflagsPCHCC_Help;
+
+extern const char kCflagsPCHObjC[];
+extern const char kCflagsPCHObjC_HelpShort[];
+extern const char* kCflagsPCHObjC_Help;
+
+extern const char kCflagsPCHObjCC[];
+extern const char kCflagsPCHObjCC_HelpShort[];
+extern const char* kCflagsPCHObjCC_Help;
+
 extern const char kCheckIncludes[];
 extern const char kCheckIncludes_HelpShort[];
 extern const char kCheckIncludes_Help[];