[gn build] (manually) port 1ee3205 more (benchmark move)

The new benchmark dep apparently has more source files than the old one.

Author: nico

llvm/utils/gn/secondary/third-party/benchmark/BUILD.gn

@@ -1,6 +1,9 @@
 static_library("benchmark") {
   sources = [
     "src/benchmark.cc",
+    "src/benchmark_api_internal.cc",
+    "src/benchmark_name.cc",
+    "src/benchmark_runner.cc",
     "src/benchmark_register.cc",
     "src/colorprint.cc",
     "src/commandlineflags.cc",
@@ -9,6 +12,7 @@ static_library("benchmark") {
     "src/counter.cc",
     "src/csv_reporter.cc",
     "src/json_reporter.cc",
+    "src/perf_counters.cc",
     "src/reporter.cc",
     "src/sleep.cc",
     "src/statistics.cc",