Add sched_getattr()/sched_setattr().

Still a questionable ABI (because the struct changes size over time without changing its name), but it's in glibc 2.41, so my assumption is that _not_ having it is likely to be more disruptive than the ABI issues going forward. (Hopefully no-one was planning on passing these structs between separately compiled libraries anyway!)

Bug: http://b/183240349
Change-Id: I80c39900b70af7e84913e547f38f656efa3e16ec
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 86dcc39..3e9f850 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1619,6 +1619,12 @@
     str2sig;
 } LIBC_V;
 
+LIBC_37 { # introduced=37
+  global:
+    sched_getattr;
+    sched_setattr;
+} LIBC_36;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86