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 5e6d53095474bd9dcaaedf8b2d818170ffb79ed7..5680beba57f042cb5f1422a80f95bb12f1dcf2d5 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -166,6 +166,15 @@ config("compiler") {
     # Common GCC compiler flags setup.
     # --------------------------------
     cflags += [ "-fno-strict-aliasing" ]  # See http://crbug.com/32204
+
+    # Eliminate build metadata (__DATE__ and __TIME_) for deterministic build.
+    # See https://crbug.com/314403
+    cflags += [
+      "-Wno-builtin-macro-redefined",

[Nico, 2016/08/24 14:41:12]

This looks pretty hacky. Can we instead teach the compiler real support for
this?

+      "-D__DATE__=",

[Nico, 2016/08/24 14:41:12]

__DATE__ and __TIME__ are supposed to be string constants. Instead of defining
them to nothing, at least define them to "", which will likely fix the ios bot.
But even then, they'll have a weird length, so maybe consider defining them to
"Oct 09 2008" and "12:34:56"

+      "-D__TIME__=",
+    ]
+
     cflags_cc += [
       # If this is removed then remove the corresponding /Zc:threadSafeInit- for
       # Windows.