exim: get rid of the convert the custom config file boolean knob

The current implementation causes troubles with the autobuilders when they
set BR2_PACKAGE_EXIM_CUSTOM_CONFIG=y, because in these cases
BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE is empty, and this is a configuration
error.

Solve the problem by entirely reomving the BR2_PACKAGE_EXIM_CUSTOM_CONFIG
boolean knob. Activation of the custon configuration file is now detected by
the fact that BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE is non-empty.

Fixes:
  http://autobuild.buildroot.org/results/0db/0db54c555f6c7e635ebf99f86b3f91dc31e441f0/

[Thomas: slightly improve commit log.]

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: bernd.kuhls@t-online.de
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/exim/Config.in

@@ -11,20 +11,16 @@ config BR2_PACKAGE_EXIM
 
 if BR2_PACKAGE_EXIM
 
-config BR2_PACKAGE_EXIM_CUSTOM_CONFIG
-	bool "Use a custom configuration file"
-	help
-	  By default Buildroot generates configuration file for exim with
-	  reasonable settings.
-	  Enable this option if you want to override the configuration file
-	  generated by Buildroot with a customized file. Then set the path
-	  to your configuration file in BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE.
-
 config BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE
 	string "Custom configuration file"
-	depends on BR2_PACKAGE_EXIM_CUSTOM_CONFIG
 	help
-	  Specify a file to use as the exim configuration file.
+	  By default, when this option is left empty, Buildroot
+	  generates a configuration file for exim with reasonable
+	  settings.
+
+	  If you want to override the configuration file generated by
+	  Buildroot with a customized file, set here the path to your
+	  configuration file with this option.
 
 	  This file shall comply with the syntax defined in the exim
 	  documentation (http://www.exim.org/docs.html).

package/exim/exim.mk

@@ -57,10 +57,7 @@ define EXIM_CONFIGURE_TOOLCHAIN
 	$(call exim-config-add,HOSTCFLAGS,$(HOSTCFLAGS))
 endef
 
-ifeq ($(BR2_PACKAGE_EXIM_CUSTOM_CONFIG),y)
-ifeq ($(call qstrip,$(BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE)),)
-$(error No exim configuration file specified, check your BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE setting)
-endif
+ifneq ($(call qstrip,$(BR2_PACKAGE_EXIM_CUSTOM_CONFIG_FILE)),)
 define EXIM_CONFIGURE_CMDS
 	$(EXIM_USE_CUSTOM_CONFIG_FILE)
 	$(EXIM_CONFIGURE_TOOLCHAIN)