@q66: replace old __sync stuff with equivalent modern ones,
so we can use libatomic on targets without atomic8 support

--- a/renderdoc/CMakeLists.txt
+++ b/renderdoc/CMakeLists.txt
@@ -55,6 +55,8 @@ elseif(UNIX)
         PRIVATE -ldl
         PRIVATE -lrt)
 
+#libatomic list(APPEND RDOC_LIBRARIES PRIVATE -latomic)
+
     if(ENABLE_XLIB)
         find_package(X11 REQUIRED)
 
--- a/renderdoc/os/posix/posix_threading.cpp
+++ b/renderdoc/os/posix/posix_threading.cpp
@@ -43,32 +43,33 @@ namespace Atomic
 {
 int32_t Inc32(int32_t *i)
 {
-  return __sync_add_and_fetch(i, int32_t(1));
+  return __atomic_add_fetch(i, int32_t(1), __ATOMIC_SEQ_CST);
 }
 
 int32_t Dec32(int32_t *i)
 {
-  return __sync_add_and_fetch(i, int32_t(-1));
+  return __atomic_sub_fetch(i, int32_t(1), __ATOMIC_SEQ_CST);
 }
 
 int64_t Inc64(int64_t *i)
 {
-  return __sync_add_and_fetch(i, int64_t(1));
+  return __atomic_add_fetch(i, int64_t(1), __ATOMIC_SEQ_CST);
 }
 
 int64_t Dec64(int64_t *i)
 {
-  return __sync_add_and_fetch(i, int64_t(-1));
+  return __atomic_sub_fetch(i, int64_t(1), __ATOMIC_SEQ_CST);
 }
 
 int64_t ExchAdd64(int64_t *i, int64_t a)
 {
-  return __sync_add_and_fetch(i, int64_t(a));
+  return __atomic_add_fetch(i, a, __ATOMIC_SEQ_CST);
 }
 
 int32_t CmpExch32(int32_t *dest, int32_t oldVal, int32_t newVal)
 {
-  return __sync_val_compare_and_swap(dest, oldVal, newVal);
+  __atomic_compare_exchange_n(dest, &oldVal, newVal, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+  return oldVal;
 }
 };