The way the makefile is set up gcc is looking for the lclntsh.so shared library in /developer/lib/.
find /developer/lib -name lclntsh.\*
to see if the shared library is where you are telling gcc to find it.
Also, you have to be logged on as the user oracle to do this, for most installs. This user normally owns those files as well.
PS all of those other libraries are going to give the same error - those things that all start with "-l"