Add a disabled builder for aarch64 emulated tests

This commit adds a disabled builder which will run all tests for the standard
library for aarch64 in a QEMU instance. Once we get enough capacity to run this
on Travis this can be used to boost our platform coverage of AArch64

src/libstd/sys/unix/process/process_common.rs

@@ -469,6 +469,7 @@ mod tests {
     // although the reason isn't very clear as to why. For now this test is
     // ignored there.
     #[cfg_attr(target_arch = "arm", ignore)]
+    #[cfg_attr(target_arch = "aarch64", ignore)]
     fn test_process_mask() {
         unsafe {
             // Test to make sure that a signal mask does not get inherited.

src/libstd/time/mod.rs

@@ -533,9 +533,17 @@ mod tests {
         assert!(b > a);
         assert_eq!(b - a, Duration::new(1, 0));
 
-        // let's assume that we're all running computers later than 2000
         let thirty_years = Duration::new(1, 0) * 60 * 60 * 24 * 365 * 30;
-        assert!(a > thirty_years);
+
+        // Right now for CI this test is run in an emulator, and apparently the
+        // aarch64 emulator's sense of time is that we're still living in the
+        // 70s.
+        //
+        // Otherwise let's assume that we're all running computers later than
+        // 2000.
+        if !cfg!(target_arch = "aarch64") {
+            assert!(a > thirty_years);
+        }
 
         // let's assume that we're all running computers earlier than 2090.
         // Should give us ~70 years to fix this!