Remove the __USE_GNU guard from pthread_setname_np again.

Caused build breakage, but not spotted by TreeHugger:

  external/libnfc-nxp/Linux_x86/phDal4Nfc.c:737:5: error: implicit declaration of function 'pthread_setname_np' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    pthread_setname_np(pthread_self(), "reader");
    ^

Nice file name.

Change-Id: I102e55718babf4e4f2f2c64066c6a83ed3ac86d3
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index c67f239..ccfd751 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -247,8 +247,9 @@
 
 #if defined(__USE_GNU)
 int pthread_getname_np(pthread_t, char*, size_t) __nonnull((2));
-int pthread_setname_np(pthread_t, const char*) __nonnull((2));
 #endif
+/* TODO: this should be __USE_GNU too. */
+int pthread_setname_np(pthread_t, const char*) __nonnull((2));
 
 int pthread_setschedparam(pthread_t, int, const struct sched_param*) __nonnull((3));