ThinLTO: workaround LLVM bug related to -nostdlib.

chrome/test/data/nacl/BUILD.gn

Index: chrome/test/data/nacl/BUILD.gn
diff --git a/chrome/test/data/nacl/BUILD.gn b/chrome/test/data/nacl/BUILD.gn
index 754e19e364de92fecbc5ee66ed1f2b796420a5b9..47b69399cc7e192a69be206d5afa04e78b3b9534 100644
--- a/chrome/test/data/nacl/BUILD.gn
+++ b/chrome/test/data/nacl/BUILD.gn
@@ -4,6 +4,7 @@
 
 import("//build/config/features.gni")
 import("//build/config/nacl/config.gni")
+import("//build/toolchain/toolchain.gni")
 import("//ppapi/native_client/nacl_test_data.gni")
 
 group("nacl") {
@@ -553,6 +554,12 @@ if (is_linux && is_clang) {
       # .exidx sections without this flag.
       "-fno-unwind-tables",
     ]
+
+    # Workaround against LLVM bug:

[Mark Seaborn, 2016/09/16 17:30:46]

Can you put the explanation that's in the commit message in this comment,
please?

[krasin1, 2016/09/16 17:54:37]

Done.

+    # https://llvm.org/bugs/show_bug.cgi?id=30403
+    if (use_thin_lto) {
+      ldflags = [ "-Wl,-plugin-opt,O0" ]
+    }
   }
 
   executable("nonsfi_libc_free_nexe") {