NaCl toolchains are too old to support Clang's -ftime-trace flag

BUG=1015750

Change-Id: Id277dc2a8a63dc1e15520cad324245fa3187aee5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1871429Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@vewd.com>
Cr-Commit-Position: refs/heads/master@{#708113}

build/config/compiler/BUILD.gn

@@ -680,7 +680,7 @@ config("compiler") {
   }
 
   if (compiler_timing) {
-    if (is_clang) {
+    if (is_clang && !is_nacl) {
       if (is_win) {
         cflags += [ "/clang:-ftime-trace" ]
       } else {