Remove exit calls from eccodes library

I am working on packaging eccodes version 2.5.0 for Fedora linux and during this work I encountered the following warnings from the rpmlint tool:

eccodes.x86_64: W: shared-lib-calls-exit /usr/lib64/libeccodes.so exit@GLIBC_2.2.5
eccodes.x86_64: W: shared-lib-calls-exit /usr/lib64/libeccodes_f90.so exit@GLIBC_2.2.5

This indicates that this library calls exit() or _exit().

Doing so from a library is usually seen as a problem.  When a library function calls exit(), it prevents the calling program from handling the error, reporting it to the user, closing files properly, and cleaning up any state that the program has. It is preferred for the library to return an actual error code and let the calling program decide how to handle the situation.