cmake : fix ARM feature verification (llama/17170)

cmake : fix ARM feature verification (llama/17170)

* cmake : fix ARM feature verification

Use check_cxx_source_compiles to prevent conflicts with
the existing GGML_NATIVE detection code.

Signed-off-by: Adrien Gallouët <redacted>
* cmake : unset __ARM_FEATURE when feature is disabled

Signed-off-by: Adrien Gallouët <redacted>
* cmake : fix scope, this is really a macro

Signed-off-by: Adrien Gallouët <redacted>
* arm_neon.h is useless

Signed-off-by: Adrien Gallouët <redacted>
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Signed-off-by: Adrien Gallouët <redacted>