lift Wno-class-memaccess

Bug: skia:9674
Change-Id: I0ed1c171b0182d168798444657c200bfeec77514
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/258269
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Ben Wagner aka dogben <benjaminwagner@google.com>

gn/BUILD.gn

@@ -350,13 +350,6 @@ config("warnings") {
     cflags_cc += [
       "-Wnon-virtual-dtor",
       "-Wno-noexcept-type",
-
-      # GCC 8+ bundles a number of fundamentally different warnings under this same flag,
-      # ranging from false positive (only copying a prefix of SkRRect from serialized form)
-      # to possibly useful (memcpy() with non-trivial types).  Annoyingly you can't really
-      # break them up any finer.
-      # TODO(mtklein): suppress / fix each site as appropriate?
-      "-Wno-class-memaccess",
     ]
   }