Clean extension build directories and exts.mk file

Author: nobu

ext/extmk.rb

@@ -722,6 +722,7 @@ def initialize(src)
     mf.puts "ECHO = $(ECHO1:0=@echo)"
     mf.puts "MFLAGS = -$(MAKEFLAGS)" if $nmake
     mf.puts "override MFLAGS := $(filter-out -j%,$(MFLAGS))" if $gnumake
+    mf.puts "ext_build_dir = #{File.dirname($command_output)}"
     mf.puts
 
     def mf.macro(name, values, max = 70)
@@ -764,6 +765,7 @@ def mf.macro(name, values, max = 70)
     mf.macro "SUBMAKEOPTS", submakeopts
     mf.macro "NOTE_MESG", %w[$(RUBY) $(top_srcdir)/tool/lib/colorize.rb skip]
     mf.macro "NOTE_NAME", %w[$(RUBY) $(top_srcdir)/tool/lib/colorize.rb fail]
+    %w[RM RMDIRS RMDIR RMALL].each {|w| mf.macro w, [RbConfig::CONFIG[w]]}
     mf.puts
     targets = %w[all install static install-so install-rb clean distclean realclean]
     targets.each do |tgt|
@@ -798,16 +800,20 @@ def mf.macro(name, values, max = 70)
       exts.each do |d|
         d = d[0..-2]
         t = "#{d}#{tgt}"
-        if  /^(dist|real)?clean$/ =~ tgt
+        if clean = /^(dist|real)?clean$/.match(tgt)
           deps = exts.select {|e|e.start_with?(d)}.map {|e|"#{e[0..-2]}#{tgt}"} - [t]
-          pd = ' ' + deps.join(' ') unless deps.empty?
+          pd = [' clean-local', *deps].join(' ')
         else
           pext = File.dirname(d)
           pd = " #{pext}/#{tgt}" if exts.include?("#{pext}/.")
         end
         mf.puts "#{t}:#{pd}\n\t$(Q)#{submake} $(MFLAGS) V=$(V) $(@F)"
+        if clean and clean.begin(1)
+          mf.puts "\t$(Q)$(RM) $(ext_build_dir)/exts.mk\n\t$(Q)$(RMDIRS) -p $(@D)"
+        end
       end
     end
+    mf.puts "\n""clean-local:\n\t$(Q)$(RM) $(ext_build_dir)/*~ $(ext_build_dir)/*.bak $(ext_build_dir)/core"
     mf.puts "\n""extso:\n"
     mf.puts "\t@echo EXTSO=$(EXTSO)"