[runtime] Use getloadavg() on NetBSD as well

Switch NetBSD from reading /proc (which is broken) to getloadavg()
(which is already used by Darwin).  NetBSD discourages using procfs
in favor of system API calls.

Differential Revision: https://reviews.llvm.org/D55486

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@348885 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/runtime/src/z_Linux_util.cpp b/runtime/src/z_Linux_util.cpp
index 283a205..c2f37eb 100644
--- a/runtime/src/z_Linux_util.cpp
+++ b/runtime/src/z_Linux_util.cpp
@@ -2065,7 +2065,7 @@
 
 #ifdef USE_LOAD_BALANCE
 
-#if KMP_OS_DARWIN
+#if KMP_OS_DARWIN || KMP_OS_NETBSD
 
 // The function returns the rounded value of the system load average
 // during given time interval which depends on the value of