Makes the ar command used deterministic.

The D flag makes ar deterministic (i.e. for the same files as inputs,
it will always produce identical outputs.

Having deterministic .a files takes us much closer to
having a fully deterministic build.

171 previously time varying .a files are now deterministic.

BUG=454642

Review URL: https://codereview.chromium.org/1595073005

Cr-Commit-Position: refs/heads/master@{#370283}

build/toolchain/gcc_toolchain.gni

@@ -228,7 +228,7 @@ template("gcc_toolchain") {
       # POSIX-like toolchains such as NaCl on Windows).
       ar_wrapper =
           rebase_path("//build/toolchain/gcc_ar_wrapper.py", root_build_dir)
-      command = "$python_path \"$ar_wrapper\" --output={{output}} --ar=\"$ar\" $arflags rcs @\"$rspfile\""
+      command = "$python_path \"$ar_wrapper\" --output={{output}} --ar=\"$ar\" $arflags rcsD @\"$rspfile\""
       description = "AR {{output}}"
       rspfile_content = "{{inputs}}"
       outputs = [