[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

llvm-svn: 348885

openmp/runtime/src/z_Linux_util.cpp

@@ -2065,7 +2065,7 @@ int __kmp_is_address_mapped(void *addr) {
 
 #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