pw_polyfill: C++11 and C++14 unit tests

Change-Id: I1a1ced2ed59a3d7dcf46c4c6a0e2e04485502fba
diff --git a/pw_build/BUILD.gn b/pw_build/BUILD.gn
index b5ad0be..9383f60 100644
--- a/pw_build/BUILD.gn
+++ b/pw_build/BUILD.gn
@@ -38,6 +38,14 @@
   cflags_cc = [ "-Wnon-virtual-dtor" ]
 }
 
+config("cpp11") {
+  cflags_cc = [ "-std=c++11" ]
+}
+
+config("cpp14") {
+  cflags_cc = [ "-std=c++14" ]
+}
+
 config("cpp17") {
   cflags_cc = [
     "-std=c++17",