Add macosx Sierra (v10.12) support to configure.

Change-Id: Ib90be26f69c658a6be6e133097c41845db58b6e1
diff --git a/README b/README
index ed9eb2b..83e57fe 100644
--- a/README
+++ b/README
@@ -72,6 +72,8 @@
     x86-darwin12-gcc
     x86-darwin13-gcc
     x86-darwin14-gcc
+    x86-darwin15-gcc
+    x86-darwin16-gcc
     x86-iphonesimulator-gcc
     x86-linux-gcc
     x86-linux-icc
@@ -87,6 +89,8 @@
     x86_64-darwin12-gcc
     x86_64-darwin13-gcc
     x86_64-darwin14-gcc
+    x86_64-darwin15-gcc
+    x86_64-darwin16-gcc
     x86_64-iphonesimulator-gcc
     x86_64-linux-gcc
     x86_64-linux-icc