jumbo: build some slow-to-compile sources separately

Daniel Bratell reports:
> v8 had a couple of files that were very slow to compile before jumbo
> and if those now end up in the same translation unit, then I can see
> how that translation unit can take an extreme time to get through
> the compiler.
>
> From one of my test builds (times in seconds):
> 49.7 v8_base/objects.o
> 44.0 v8_base/code-stub-assembler.o
> 32.9 v8_base/api.o
> 30.5 v8_base/elements.o
> 25.9 v8_builtins_generators/builtins-regexp-gen.o
> 22.8 v8_base/parser.o
> 21.2 v8_base/heap.o
>
> All of these are in the slowest 0.1% ninja jobs so they are extreme
> in some way. I think I would just exclude them all (or at least the
> 30s+ ones) completely from jumbo.

BUG=chromium:746958

Change-Id: I01741109def4f9ac7c946319374076eb7b9d03b6
Reviewed-on: https://chromium-review.googlesource.com/637971
Commit-Queue: Mostyn Bramley-Moore <mostynb@opera.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47703}

BUILD.gn

@@ -1038,6 +1038,10 @@ v8_source_set("v8_builtins_generators") {
       # TODO(mostynb@opera.com): don't exclude these http://crbug.com/752428
       "src/builtins/builtins-async-iterator-gen.cc",
       "src/builtins/builtins-async-generator-gen.cc",
+
+      # This source file takes an unusually large amount of time to
+      # compile.  Build it separately to avoid bottlenecks.
+      "src/builtins/builtins-regexp-gen.cc",
     ]
   }
 
@@ -2075,6 +2079,15 @@ v8_source_set("v8_base") {
     jumbo_excluded_sources = [
       # TODO(mostynb@opera.com): don't exclude these http://crbug.com/752428
       "src/profiler/heap-snapshot-generator.cc",  # Macro clash in mman-linux.h
+
+      # These source files take an unusually large amount of time to
+      # compile.  Build them separately to avoid bottlenecks.
+      "src/api.cc",
+      "src/code-stub-assembler.cc",
+      "src/elements.cc",
+      "src/heap/heap.cc",
+      "src/objects.cc",
+      "src/parsing/parser.cc",
     ]
   }