Move default barrier implementation to KernelIntrinsics

Author: christiangnrd

src/KernelAbstractions.jl

@@ -819,7 +819,7 @@ function SharedMemory(t::Type{T}, dims::Val{Dims}, id::Val{Id}) where {T, Dims,
 end
 
 function __synchronize()
-    error("@synchronize used outside kernel or not captured")
+    KernelIntrinsics.barrier()
 end
 
 @generated function __print(items...)

src/intrinsics.jl

@@ -52,7 +52,9 @@ Returns the unique group ID.
 function get_group_id end
 
 function localmemory end
-function barrier end
+function barrier()
+    error("Group barrier used outside kernel or not captured")
+end
 function print end
 
 end