Revert of No threadsafe statics. (patchset #1 id:1 of https://codereview.chromium.org/654663002/)

Reason for revert:
Want to think about how to do this only to skialib and not to tools (gms, tests, etc.)

Original issue's description:
> No threadsafe statics.
>
> Chrome disables these for speed and code size, so we need
> to disable them to make sure our code is safe when used
> this way.
>
>     int foo() {
>         static int32_t atomic_thing;
>         return sk_atomic_inc(&atomic_thing);
>     }
>
> is not safe in Chrome.  Making the static global is:
>
>     static int32_t atomic_thing;
>     int foo() {
>         return sk_atomic_inc(&atomic_thing);
>     }
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/cad5d3e264535c919b80e1e2a85407307961f221

TBR=bungeman@google.com,mtklein@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/649343003

gyp/common_conditions.gypi

@@ -202,7 +202,6 @@
         ],
         'cflags_cc': [
           '-fno-rtti',
-          '-fno-threadsafe-statics',  # Chrome disables this, so for safety we should too.
           '-Wnon-virtual-dtor',
           '-Wno-invalid-offsetof',  # GCC <4.6 is old-school strict about what is POD.
         ],