Enable ThinLTO for POSIX LTO by default on Linux, take 2.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 475 matching lines @@
       ldflags += [ "-flto=thin" ]
 
       # Limit the parallelism to avoid too agressive competition between
       # linker jobs. This is still suboptimal to a potential dynamic
       # resource allocation scheme, but should be good enough.
       if (use_lld) {
         ldflags += [
           "-Wl,--thinlto-jobs=8",
           "-Wl,--thinlto-cache-dir=" +
               rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
+
+          # Limit the size of the ThinLTO cache to 10% of available disk space.
+          # TODO(pcc): Change the limit from a percentage to an absolute size
+          # (10-20GB) once that feature lands in LLVM.
+          "-Wl,--thinlto-cache-policy,cache_size=10%",
         ]
       } else {
         ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
       }
 
       # Disable optimization for now because they increase binary size by too
       # much.
       if (is_linux && use_lld) {
         ldflags += [ "-Wl,--lto-O0" ]
       }
@@ skipping 1300 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }