I'm getting an error when attempting to run sudo gem install captured with the following tail:
gcc -I. -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin11.0 -I. -DRUBY_EXTCONF_H="curb_config.h" -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE -fno-common -pipe -fno-common -I/opt/local/include -g -Wall -c curb.c
In file included from /opt/local/include/curl/curl.h:35,
/opt/local/include/curl/curlrules.h:143: error: size of array ‘curl_rule_01’ is negative
/opt/local/include/curl/curlrules.h:153: error: size of array ‘curl_rule_02’ is negative
lipo: can't open input file: /var/tmp//ccGv23da.out (No such file or directory)
make: *** [curb.o] Error 1
Seems like there is a problem with the version of curl you have and the default ruby on OS X -- what version do you have installed? Does it match what is in installed with ports?
You might do better to build against the system libcurl.