Add getloadavg(3).

Lets us build ninja with bionic.

Bug: N/A
Test: ran tests
Change-Id: I97eef1247d794b58a2b9aee4851551632e5a4e48
diff --git a/libc/libc.arm64.map b/libc/libc.arm64.map
index 55fd587..81ff00d 100644
--- a/libc/libc.arm64.map
+++ b/libc/libc.arm64.map
@@ -1353,6 +1353,7 @@
     android_fdsan_get_error_level;
     android_fdsan_set_error_level;
     android_get_device_api_level;
+    getloadavg;
     pthread_sigqueue;
     reallocarray;
     timespec_get;