[lib][cmpctmalloc] mark cmpctmalloc as needing float

It's just a test routine that's using floating point, but since nothing
in cmpctmalloc should be used in interrupt context, it should be okay to
mark this code as using float.

lib/heap/cmpctmalloc/rules.mk

@@ -5,4 +5,8 @@ MODULE := $(LOCAL_DIR)
 MODULE_SRCS += \
 	$(LOCAL_DIR)/cmpctmalloc.c
 
+# cmpct_test_trim() uses some floating point
+# TODO: move tests to another file to avoid this
+MODULE_OPTIONS := float
+
 include make/module.mk