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:

Review URL: https://codereview.chromium.org/654663002

gyp/common_conditions.gypi

@@ -202,6 +202,7 @@
         ],
         '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.
         ],