Add nproc from toybox

Change-Id: Ic09e00047c046fb60bb448811211e49720d1f579
(cherry picked from commit 6c691cf2114a4721022eb4154c31f0a67debc048)
diff --git a/darwin-x86/bin/nproc b/darwin-x86/bin/nproc
new file mode 120000
index 0000000..0196b74
--- /dev/null
+++ b/darwin-x86/bin/nproc
@@ -0,0 +1 @@
+../../../build-tools/darwin-x86/bin/toybox
\ No newline at end of file
diff --git a/linux-x86/bin/nproc b/linux-x86/bin/nproc
new file mode 120000
index 0000000..1e6ef39
--- /dev/null
+++ b/linux-x86/bin/nproc
@@ -0,0 +1 @@
+../../../build-tools/linux-x86/bin/toybox
\ No newline at end of file