Add LATEST_ERLANG_OTP=1 to automatically select the latest build

I need this for CI because I want to run Dialyzer only against
the most recent OTP after tests have passed everywhere. Left
undocumented for now.

[ci skip]

core/kerl.mk

@@ -48,6 +48,10 @@ distclean-kerl:
 
 # Allow users to select which version of Erlang/OTP to use for a project.
 
+ifneq ($(strip $(LATEST_ERLANG_OTP)),)
+ERLANG_OTP := $(notdir $(lastword $(sort $(wildcard $(KERL_INSTALL_DIR)/*[^-native]))))
+endif
+
 ERLANG_OTP ?=
 ERLANG_HIPE ?=