I noticed a previous reply saying that it's caused by ./autogen.sh's failure to detect it's location, but I've opened autogen.sh and cannot figure out what needs to be done.
$ CFLAGS="-O3 -Wall -msse2" ./configure
...
./configure: line 4598: syntax error near unexpected token `,'
./configure: line 4598: `LIBCURL_CHECK_CONFIG(, 7.10.1, ,'
Yes, this is a FAQ. Use the tarball, not git repo, for building.