Add missing config to fuzzer_support gn rules

BUG=
R=yangguo@chromium.org, machenbach@chromium.org

Review URL: https://codereview.chromium.org/1748393002 .

Cr-Commit-Position: refs/heads/master@{#34390}

BUILD.gn

@@ -1844,6 +1844,7 @@ source_set("fuzzer_support") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config_base",
+    ":libplatform_config",
     ":features",
     ":toolchain",
   ]