gc, runtime: handle floating point map keys

Fixes #2609.

R=ken2
CC=golang-dev
https://golang.org/cl/5572069
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index a30a16c..df2cd14 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -375,6 +375,10 @@
 	AINTER,
 	ANILINTER,
 	ASLICE,
+	AFLOAT32,
+	AFLOAT64,
+	ACPLX64,
+	ACPLX128,
 	Amax
 };
 typedef	struct	Alg		Alg;