cmake : simplify build info detection using standard variables (#17423)

The current approach has several drawbacks. Mostly, when
cross-compiling, invoking the compiler binary directly to query the
machine hardware can behave unexpectedly depending on the toolchain
wrapper (using COMPILER_TARGET, CFLAGS, etc).

As CMake is the official tool to build llama.cpp, I propose to only rely
on it to get those variables (`CMAKE_SYSTEM_NAME` and
`CMAKE_SYSTEM_PROCESSOR`).

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

cmake/build-info.cmake

@@ -39,26 +39,10 @@ if(Git_FOUND)
     endif()
 endif()
 
-if(MSVC)
-    set(BUILD_COMPILER "${CMAKE_C_COMPILER_ID} ${CMAKE_C_COMPILER_VERSION}")
-    if (CMAKE_VS_PLATFORM_NAME)
-        set(BUILD_TARGET ${CMAKE_VS_PLATFORM_NAME})
-    else()
-        set(BUILD_TARGET "${CMAKE_SYSTEM_NAME} ${CMAKE_SYSTEM_PROCESSOR}")
-    endif()
-else()
-    execute_process(
-        COMMAND ${CMAKE_C_COMPILER} --version
-        OUTPUT_VARIABLE OUT
-        OUTPUT_STRIP_TRAILING_WHITESPACE
-    )
-    string(REGEX REPLACE " *\n.*" "" OUT "${OUT}")
-    set(BUILD_COMPILER ${OUT})
+set(BUILD_COMPILER "${CMAKE_C_COMPILER_ID} ${CMAKE_C_COMPILER_VERSION}")
 
-    execute_process(
-        COMMAND ${CMAKE_C_COMPILER} -dumpmachine
-        OUTPUT_VARIABLE OUT
-        OUTPUT_STRIP_TRAILING_WHITESPACE
-    )
-    set(BUILD_TARGET ${OUT})
+if(CMAKE_VS_PLATFORM_NAME)
+    set(BUILD_TARGET ${CMAKE_VS_PLATFORM_NAME})
+else()
+    set(BUILD_TARGET "${CMAKE_SYSTEM_NAME} ${CMAKE_SYSTEM_PROCESSOR}")
 endif()