Add a usability check

[coatless]

Maybe also check to see if a set of header files (cmath, iterators, ...) are present to ensure the CLI is correctly setup.

Related: RcppCore/Rcpp#1333 (comment)

[coatless]

This is technically what pkgbuild::check_build_tools() does via has_compiler():

function (debug = FALSE) 
{
    res <- getOption("pkgbuild.has_compiler")
    if (!is.null(res)) {
        if (is_flag(res)) 
            return(res)
        stop(cli::format_error(c("", `!` = "Invalid {.code pkgbuild.has_compiler} option.", 
            i = "It must be {.code TRUE} or {.code FALSE}, not {.type {res}}.")))
    }
    if (!debug && cache_exists("has_compiler")) {
        return(cache_get("has_compiler"))
    }
    foo_path <- file.path(tempdir(), "foo.c")
    cat("void foo(int *bar) { *bar=1; }\n", file = foo_path)
    on.exit(unlink(foo_path))
    res <- tryCatch({
        if (debug) {
            message("Trying to compile a simple C file")
        }
        callr::rcmd_safe("SHLIB", "foo.c", wd = tempdir(), show = debug, 
            echo = debug, fail_on_status = TRUE, stderr = "2>&1")
        if (debug) {
            message("")
        }
        dylib <- file.path(tempdir(), paste0("foo", .Platform$dynlib.ext))
        on.exit(unlink(dylib), add = TRUE)
        dll <- dyn.load(dylib)
        on.exit(dyn.unload(dylib), add = TRUE)
        .C(dll$foo, 0L)[[1]] == 1L
    }, error = function(e) {
        FALSE
    })
    cache_set("has_compiler", res)
    res
}