cmake try_compile(SOURCE_FROM_CONTENT) examples

YosysHQ/nextpnr cmake/CheckCXXCompilerHashEmbed.cmake :12

try_compile(
    ${VAR}
    SOURCE_FROM_CONTENT
        compiletest.cc
        "const char s[] = {\n#embed \"${CMAKE_CURRENT_FUNCTION_LIST_FILE}\"\n};\nint main() {}"
)