install path

If you don't use configure's --prefix option, the default installation will happen in /usr/local so curl ends up at /usr/local/bin/curl.

symbol lookup error

The symbol it reports to be missing is a recent addition to libcurl, which indicates that you're invoking a new curl tool that loads and uses an older libcurl - ie not the one you just installed but one from a previous (system?) install.

You can verify which libcurl your curl loads by invoking

$ ldd /usr/local/bin/curl | grep libcurl

You can change which libcurl your curl loads in one of several way, neither of which is curl specific so I'll just briefly mention the methods here to be further explained elsewhere:

1. Just set LD_LIBRARY_PATH in the shell before you invoke curl
2. Edit /etc/ld.so.conf and make sure the order of the search path makes the new libcurl gets found before the old one.
3. Link your curl executable with a hard coded path to the new libcurl by invoking configure with something like LDFLAGS=-Wl,-R/usr/local/ssl/lib ./configure ...

replacing the system library?

It is generally not advised to replace the system installed libcurl with your custom build. Mostly because you might have an application or two that depend on specifics of that build. When you install your own libcurl from source, it is generally better to keep it installed in a separate path so that it can co-exist with the one already installed in your syste,.