libgo: additional type/const references in sysinfo.c

Add a few more explicit references to enumeration constants
(RUSAGE_SELF, DT_UNKNOWN) in sysinfo.c to insure that their hosting enums
are emitted into DWARF, when using a clang host compiler during
the gollvm build.

Updates golang/go#41382.
Updates golang/go#41404.

Change-Id: Id0ed7a82ae5dc98ccffa5269a7147e0171c9b0ea
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/254941
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Than McIntosh <thanm@google.com>
diff --git a/libgo/sysinfo.c b/libgo/sysinfo.c
index 0692fd4..7640559 100644
--- a/libgo/sysinfo.c
+++ b/libgo/sysinfo.c
@@ -316,6 +316,7 @@
 SREF(dirent);
 SREF(dirent64);
 OTREF(DIR);
+EREF(DT_UNKNOWN);
 
 // From fcntl.h
 SREF(flock);
@@ -437,6 +438,7 @@
 SREF(rlimit64);
 EREF(RLIMIT_NOFILE);
 EREF(PRIO_USER);
+EREF(RUSAGE_SELF);
 
 // From sys/select.h
 TREF(fd_set);