support file extension .cpp/.cxx in mrbgem and tool

Rakefile

@@ -53,7 +53,7 @@ MRuby.each_target do |target|
 
     gem.bins.each do |bin|
       exec = exefile("#{build_dir}/bin/#{bin}")
-      objs = Dir.glob("#{current_dir}/tools/#{bin}/*.c").map { |f| objfile(f.pathmap("#{current_build_dir}/tools/#{bin}/%n")) }
+      objs = Dir.glob("#{current_dir}/tools/#{bin}/*.{c,cpp,cxx}").map { |f| objfile(f.pathmap("#{current_build_dir}/tools/#{bin}/%n")) }
 
       file exec => objs + [libfile("#{build_dir}/lib/libmruby")] do |t|
         gem_flags = gems.map { |g| g.linker.flags }

tasks/mrbgem_spec.rake

@@ -53,13 +53,13 @@ module MRuby
         @linker = LinkerConfig.new([], [], [], [])
 
         @rbfiles = Dir.glob("#{dir}/mrblib/*.rb").sort
-        @objs = Dir.glob("#{dir}/src/*.{c,cpp,m,asm,S}").map do |f|
+        @objs = Dir.glob("#{dir}/src/*.{c,cpp,cxx,m,asm,S}").map do |f|
           objfile(f.relative_path_from(@dir).to_s.pathmap("#{build_dir}/%X"))
         end
         @objs << objfile("#{build_dir}/gem_init")
 
         @test_rbfiles = Dir.glob("#{dir}/test/*.rb")
-        @test_objs = Dir.glob("#{dir}/test/*.{c,cpp,m,asm,S}").map do |f|
+        @test_objs = Dir.glob("#{dir}/test/*.{c,cpp,cxx,m,asm,S}").map do |f|
           objfile(f.relative_path_from(dir).to_s.pathmap("#{build_dir}/%X"))
         end
         @test_preload = 'test/assert.rb'