Use stdatomic instead of gcc-internal atomics

The __atomic operations are internal to gcc and not necessarily supported
by all c11 compilers. Use the atomics in stdatomic instead.

Signed-off-by: Nathan Hjelm <hjelmn@google.com>

libusb/libusbi.h

diff --git a/libusb/libusbi.h b/libusb/libusbi.h
index aea1bac..7656660 100644
--- a/libusb/libusbi.h
+++ b/libusb/libusbi.h
@@ -103,11 +103,12 @@
 #define usbi_atomic_inc(a)	InterlockedIncrement((a))
 #define usbi_atomic_dec(a)	InterlockedDecrement((a))
 #else
-typedef long usbi_atomic_t;
-#define usbi_atomic_load(a)	__atomic_load_n((a), __ATOMIC_SEQ_CST)
-#define usbi_atomic_store(a, v)	__atomic_store_n((a), (v), __ATOMIC_SEQ_CST)
-#define usbi_atomic_inc(a)	__atomic_add_fetch((a), 1, __ATOMIC_SEQ_CST)
-#define usbi_atomic_dec(a)	__atomic_sub_fetch((a), 1, __ATOMIC_SEQ_CST)
+#include <stdatomic.h>
+typedef atomic_long usbi_atomic_t;
+#define usbi_atomic_load(a)	atomic_load((a))
+#define usbi_atomic_store(a, v)	atomic_store((a), (v))
+#define usbi_atomic_inc(a)	(atomic_fetch_add((a), 1) + 1)
+#define usbi_atomic_dec(a)	(atomic_fetch_add((a), -1) - 1)
 #endif
 
 /* Internal abstractions for event handling and thread synchronization */

libusb/version_nano.h

diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index 6926971..40532d3 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 11587
+#define LIBUSB_NANO 11588