Make __DATE__ and __TIME__ to evaluate to an empty string.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index a319d6028603d977e05156ddeafa20fe588e4f08..f7e0702cddf758cbc899470e4674834254052bec 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -78,6 +78,11 @@ declare_args() {
   # of binutils can cause linker warning.
   # See: https://bugs.chromium.org/p/chromium/issues/detail?id=457359
   fatal_linker_warnings = true
+
+  # Keep build metadata (__DATE__ and __TIME_) available.
+  # For the deterministic build, these parameters should be eliminated.
+  # See:  https://bugs.chromium.org/p/chromium/issues/detail?id=314403
+  enable_date_time_builtin_macro = false

[Dirk Pranke, 2016/08/22 17:31:45]

Does this even need to be easily toggleable? Why not just unconditionally set
the flags on line 217?

[M-A Ruel, 2016/08/22 19:16:53]

That's my opinion too, no need for a flag. Less flag is better.

[Yoshisato Yanagisawa, 2016/08/23 01:37:54]

I do not have strong opinions on whether to make it flags or not make it flags. 
Currently, __DATE__ seems only show up to flatc and I do not think it meaningful
to show actual date there.
Let me force the metadata eliminated.

 }
 
 if (is_clang && !is_nacl) {
@@ -207,6 +212,14 @@ config("compiler") {
       # crbug.com/485542
       ldflags += [ "-Wl,--fatal-warnings" ]
     }
+
+    if (!enable_date_time_builtin_macro) {
+      cflags += [
+        "-Wno-builtin-macro-redefined",
+        "-D__DATE__=",
+        "-D__TIME__=",
+      ]
+    }
   }
 
   if (is_clang && is_debug) {