Minimize AtFork deps

Summary: [Folly] Minimize `AtFork` deps by using removing use of `checkPosixError`. The owning library is a bit heavyweight.

Reviewed By: simpkins

Differential Revision: D8109884

fbshipit-source-id: a0a41ff64fd44b843970ae30f8fdb8ff4ff22acd

folly/detail/AtFork.cpp

@@ -13,12 +13,14 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 #include <folly/detail/AtFork.h>
 
 #include <list>
 #include <mutex>
 
-#include <folly/Exception.h>
+#include <folly/lang/Exception.h>
+#include <folly/portability/PThread.h>
 
 namespace folly {
 
@@ -83,7 +85,10 @@ class AtForkList {
 #if FOLLY_HAVE_PTHREAD_ATFORK
     int ret = pthread_atfork(
         &AtForkList::prepare, &AtForkList::parent, &AtForkList::child);
-    checkPosixError(ret, "pthread_atfork failed");
+    if (ret != 0) {
+      throw_exception<std::system_error>(
+          ret, std::generic_category(), "pthread_atfork failed");
+    }
 #elif !__ANDROID__ && !defined(_MSC_VER)
 // pthread_atfork is not part of the Android NDK at least as of n9d. If
 // something is trying to call native fork() directly at all with Android's