tree-wide: replace FLAGS_SET(..., 1 << v) with BIT_SET(..., v)

src/core/execute.c

@@ -20,6 +20,7 @@
 #include "af-list.h"
 #include "alloc-util.h"
 #include "async.h"
+#include "bitfield.h"
 #include "cap-list.h"
 #include "capability-util.h"
 #include "cgroup-setup.h"
@@ -1666,7 +1667,7 @@ int exec_context_get_clean_directories(
         assert(ret);
 
         for (ExecDirectoryType t = 0; t < _EXEC_DIRECTORY_TYPE_MAX; t++) {
-                if (!FLAGS_SET(mask, 1U << t))
+                if (!BIT_SET(mask, t))
                         continue;
 
                 if (!prefix[t])