cmake : allow repeated find_package calls for llama

[miyanyan]

Overview

cmake : allow repeated find_package calls for llama

Additional information

currently llama-cpp doesn't export targets in cmake, like:

install(TARGETS llama EXPORT llama-targets ...)
install(EXPORT llama-targets ...)

if add this, we can easily use

include("${CMAKE_CURRENT_LIST_DIR}/llama-targets.cmake")

in config.cmake

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, found this issue in [ggml, llama-cpp] Update to 0.24.0 and 0.4.1 microsoft/vcpkg#53995