[C++] Update grep for CPU count.

Author: mjpt777

cppbuild/cppbuild

@@ -10,7 +10,7 @@ case "$(uname)" in
     ncpus=$(sysctl -n hw.ncpu)
     ;;
   Linux*)
-    ncpus=$(lscpu -p | egrep -v '^#' | wc -l)
+    ncpus=$(lscpu -p | grep -c -E -v '^#')
     ;;
 esac