我在Ubuntu 15.04上安装syck时遇到错误。构建本机扩展失败：
Installing syck 1.0.1 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
/home/markus/.rvm/rubies/ruby-2.2.1/bin/ruby -r ./siteconf20150618-8242-1z0c5iw.rb extconf.rb
checking for st.h... yes
creating Makefile
make "DESTDIR=" clean
make "DESTDIR="
compiling bytecode.c
compiling implicit.c
compiling token.c
token.re: In function ‘sycklex_yaml_utf8’:
token.re:541:36: warning: variable ‘lvl’ set but not used [-Wunused-but-set-variable]
compiling rubyext.c
rubyext.c:31:20: error: field ‘hash’ has incomplete type
struct RHash hash;
^
rubyext.c: In function ‘syck_seq_initialize’:
rubyext.c:1529:15: warning: variable ‘node’ set but not used [-Wunused-but-set-variable]
SyckNode *node;
^
Makefile:237: recipe for target 'rubyext.o' failed
make: *** [rubyext.o] Error 1
make failed, exit code 2
Gem files will remain installed in /home/markus/.rvm/gems/ruby-2.2.1@mygemset/gems/syck-1.0.1 for inspection.
Results logged to /home/markus/.rvm/gems/ruby-2.2.1@mygemset/extensions/x86_64-linux/2.2.0/syck-1.0.1/gem_make.out
An error occurred while installing syck (1.0.1), and Bundler cannot continue.
Make sure that `gem install syck -v '1.0.1'` succeeds before bundling.
是否有人知道问题是什么以及如何解决？