update HIP doc

Author: Jason-VanBeusekom

clang/docs/HIPSupport.rst

@@ -293,6 +293,7 @@ Clang supports alias attributes in HIP code, allowing creation of alternative na
  - Aliases work with ``__host__``, ``__device__``, and ``__host__ __device__`` functions and variables.
  - The alias attribute uses the syntax ``__attribute__((alias("target_name")))``. Both weak and strong aliases are supported.
  - Outside of ``extern "C"``, the alias target must use the mangled name of the aliasee
+ - The alias is only emitted if the aliasee is emitted on the same side (ie __host__ or __device__), otherwise it is ignored.
 
 Example Usage
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