Separate L4Re code, add aarch64 and enable tests

The L4Re code was previously attached to the Linux code which was not
correct in many ways. This commit separates the L4Re code and enables
the libc-tests and includes the fixes for the failing tests. Aarch64 is
added as a second supported architecture (more to come).

Author: farao

ctest/src/lib.rs

@@ -1070,6 +1070,8 @@ fn default_cfg(target: &str) -> Vec<(String, Option<String>)> {
         ("hurd", "unix", "gnu")
     } else if target.contains("cygwin") {
         ("cygwin", "unix", "")
+    } else if target.contains("l4re-uclibc") {
+        ("l4re", "unix", "uclibc")
     } else {
         panic!("unknown os/family: {}", target)
     };