Make the atomic load explicit

Technically, std::atomic does not have an operator(). Previously, this
code was relying on an implicit behavior of our C++ standard library in
order to compile. When compiling this code against a different C++
standard library, I encountered a compiler error on these lines.

This CL makes the std::atomic load() operation explicit, makes it
clearer what this code is actually doing and makes it conform better to
the C++ standard library spec rather than a particular implmentation.

Change-Id: I7f255dffc0a3d8e07c973c18e9ba4098c4b5843e
diff --git a/libc/bionic/recvmsg.cpp b/libc/bionic/recvmsg.cpp
index 003f43d..4d3f989 100644
--- a/libc/bionic/recvmsg.cpp
+++ b/libc/bionic/recvmsg.cpp
@@ -39,7 +39,7 @@
 
 static inline __attribute__((artificial)) __attribute__((always_inline)) void track_fds(
     struct msghdr* msg, const char* function_name) {
-  if (!__android_fdtrack_hook) {
+  if (!atomic_load(&__android_fdtrack_hook)) {
     return;
   }
 
diff --git a/libc/private/bionic_fdtrack.h b/libc/private/bionic_fdtrack.h
index 752dd8d..259897c 100644
--- a/libc/private/bionic_fdtrack.h
+++ b/libc/private/bionic_fdtrack.h
@@ -58,7 +58,7 @@
         event.fd = __fd;                                          \
         event.type = ANDROID_FDTRACK_EVENT_TYPE_CREATE;           \
         event.data.create.function_name = name;                   \
-        __android_fdtrack_hook(&event);                           \
+        atomic_load(&__android_fdtrack_hook)(&event);             \
         tls.fdtrack_disabled = false;                             \
       }                                                           \
     }                                                             \
@@ -86,7 +86,7 @@
         android_fdtrack_event event;                             \
         event.fd = __fd;                                         \
         event.type = ANDROID_FDTRACK_EVENT_TYPE_CLOSE;           \
-        __android_fdtrack_hook(&event);                          \
+        atomic_load(&__android_fdtrack_hook)(&event);            \
         tls.fdtrack_disabled = false;                            \
         errno = saved_errno;                                     \
       }                                                          \