If you've done a previous "install Imager" in that CPAN session it won't attempt to do the build again but just complain like the above.

First step would be to start a new CPAN session and try "install Imager" again, and post the results of that.

If that produces the same results try doing it manually, from CPAN do:

And then post the results of that.

Depending on how your system is setup a number of different components could be missing, including make, compilers, binutils, build-time libraries/headers. The look/perl Makefile.PL/make should reveal which it is.