cmake : use list(APPEND ...) instead of set() + dedup linker (llama/9463)

cmake : use list(APPEND ...) instead of set() + dedup linker (llama/9463)

* cmake : use list(APPEND ...) instead of set() + dedup linker

ggml-ci

* cmake : try fix sycl

* cmake : try to fix sycl 2

* cmake : fix sycl build (llama/9469)

* try fix sycl build

* use CMAKE_CXX_FLAGS as a string variable

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Co-authored-by: Georgi Gerganov <redacted>
* one more CMAKE_CXX_FLAGS fix (llama/9471)

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Co-authored-by: Michael Podvitskiy <redacted>