Only check for erlang release when copying .app file

This way we avoid the cost of checking it on every command.
When copying the .app file must be enough as we'd change
the Erlang requirement only on new versions.

Author: José Valim

Makefile

@@ -3,7 +3,6 @@ ELIXIRC := bin/elixirc --verbose --ignore-module-conflict
 ERLC := erlc -I lib/elixir/include
 ERL := erl -I lib/elixir/include -noshell -pa lib/elixir/ebin
 VERSION := $(strip $(shell cat VERSION))
-MIN_ERLANG_VERSION := 17
 Q := @
 PREFIX := /usr/local
 LIBDIR := lib
@@ -15,7 +14,17 @@ INSTALL_PROGRAM = $(INSTALL) -m755
 .PHONY: install compile erlang elixir dialyze test clean docs release_docs release_zip check_erlang_release
 .NOTPARALLEL: compile
 
-#==> Templates
+#==> Functions
+
+# This check should work for older versions like R16B
+# as well as new verions like 17.1 and 18
+define CHECK_ERLANG_RELEASE
+	$(Q) erl -noshell -eval 'io:fwrite("~s", [erlang:system_info(otp_release)])' -s erlang halt | grep -q '^1[789]'; \
+		if [ $$? != 0 ]; then                                                                                        \
+		   echo "At least Erlang 17.0 is required to build Elixir";                                                  \
+		   exit 1;                                                                                                   \
+		fi;
+endef
 
 define APP_TEMPLATE
 $(1): lib/$(1)/ebin/Elixir.$(2).beam lib/$(1)/ebin/$(1).app
@@ -44,18 +53,10 @@ UNICODE:=lib/elixir/ebin/Elixir.String.Unicode.beam
 
 default: compile
 
-compile: check_erlang_release lib/elixir/src/elixir.app.src erlang elixir
-
-# this check should work for older versions like R16B
-# as well as new verions like 17.1 and 18
-check_erlang_release:
-	 @ erl -noshell -eval 'io:fwrite("~s", [erlang:system_info(otp_release)])' -s erlang halt | grep -q '^1[789]'; \
-		if [ $$? != 0 ]; then                                                                                      \
-		   echo "At least Erlang 17.0 is required to build Elixir";                                                \
-		   exit 1;                                                                                                 \
-		fi
+compile: lib/elixir/src/elixir.app.src erlang elixir
 
 lib/elixir/src/elixir.app.src: src/elixir.app.src
+	$(Q) $(call CHECK_ERLANG_RELEASE)
 	$(Q) rm -rf lib/elixir/src/elixir.app.src
 	$(Q) echo "%% This file is automatically generated from <project_root>/src/elixir.app.src" \
 	                             >lib/elixir/src/elixir.app.src

lib/elixir/rebar.config

@@ -21,5 +21,3 @@
             {report, true},
             {verbose, false}
            ]}.
-
-{require_otp_vsn,"(17).*"}.