Replace mere enable_debug by clearer conf.enable_debug [ci skip]

build_config/host-cxx.rb

@@ -1,7 +1,6 @@
 MRuby::Build.new do |conf|
   toolchain :gcc
 
-  enable_debug
   # include the default GEMs
   conf.gembox 'default'
 

build_config/host-debug.rb

@@ -8,7 +8,7 @@ MRuby::Build.new('host') do |conf|
     toolchain :gcc
   end
 
-  enable_debug
+  conf.enable_debug
 
   # include the default GEMs
   conf.gembox 'full-core'

build_config/host-gprof.rb

@@ -9,6 +9,6 @@ MRuby::Build.new do |conf|
   conf.linker.flags << '-pg'
 
   # Turn on `enable_debug` for better debugging
-  enable_debug
+  conf.enable_debug
   conf.enable_test
 end

build_config/host-shared.rb

@@ -30,7 +30,7 @@ MRuby::Build.new do |conf|
   # conf.file_separator = '/'
 
   # Turn on `enable_debug` for better debugging
-  enable_debug
+  conf.enable_debug
   conf.enable_bintest
   conf.enable_test
 end

build_config/travis.rb

@@ -1,6 +1,6 @@
 MRuby::Build.new('full-debug') do |conf|
   toolchain :gcc
-  enable_debug
+  conf.enable_debug
 
   # include all core GEMs
   conf.gembox 'full-core'

mrbgems/mruby-method/README.md

@@ -15,7 +15,7 @@ You need to enable debug option in your build configuration to use
 
 ```ruby
 MRuby::Build.new do |conf|
-  enable_debug
+  conf.enable_debug
 end
 ```