Add more values for (os/which)

Some bsd flavors.

auxlib/cook.janet

@@ -296,11 +296,12 @@
   (def lflags [;(opt opts :lflags default-lflags)
                ;(if (opts :static) [] dynamic-lflags)
                ;(if standalone (case (os/which)
-                                :posix ["-ldl" "-lm"]
                                 :macos ["-ldl" "-lm"]
                                 :windows []
                                 :linux ["-lm" "-ldl" "-lrt"]
-                                []) [])])
+                                :openbsd ["-lm"]
+                                #default
+                                ["-ldl" "-lm"]) [])])
   (rule target objects
         (print "linking " target "...")
         (if is-win

src/core/os.c

@@ -75,6 +75,12 @@ static Janet os_which(int32_t argc, Janet *argv) {
     return janet_ckeywordv("web");
 #elif defined(__linux__)
     return janet_ckeywordv("linux");
+#elif define(__FreeBSD__)
+    return janet_ckeywordv("freebsd");
+#elif define(__NetBSD__)
+    return janet_ckeywordv("netbsd");
+#elif define(__OpenBSD__)
+    return janet_ckeywordv("openbsd");
 #else
     return janet_ckeywordv("posix");
 #endif
@@ -763,10 +769,13 @@ static const JanetReg os_cfuns[] = {
         "os/which", os_which,
         JDOC("(os/which)\n\n"
              "Check the current operating system. Returns one of:\n\n"
-             "\t:windows - Microsoft Windows\n"
-             "\t:macos - Apple macos\n"
+             "\t:windows\n"
+             "\t:macos\n"
              "\t:web - Web assembly (emscripten)\n"
-             "\t:linux - Linux\n"
+             "\t:linux\n"
+             "\t:freebsd\n"
+             "\t:openbsd\n"
+             "\t:netbsd\n"
              "\t:posix - A POSIX compatible system (default)")
     },
     {