Disable use options if libs not available

[austincrosswx]

When cmake options for several libraries are enabled, check if the libraries were found and disable the compilation option if not, rather that using REQUIRED so that compilation can continue (e.g. compile with OpenMP or ipolates if available and without if not).

This should make it a bit simpler to stick with the defaults and use whatever is available on a particular system, instead of always explicitly setting features to enable prior to build. Hopefully not confusing for users expecting an specifically enabled feature to fail; could maybe switch to using what is available then and specifically verifying requested options?

Added for iplib (ipolates), NetCDF, Jasper, OpenJPEG, OpenMP

(Hello from Aviation Weather Center!)

[edwardhartnett]

We prefer that if the compile options be checked for success. In other words, when wgrib2 is compiled, and the builder wants to use the ip library, if the ip library is not present, the builder needs to know that. So if we make the build system too smart, then wgrib2 will be built in a way different from that which was intended, which could lead to confusion later.

So, builders need to know whether or not they want to use the ip library, and that is enforced by cmake.