nco fails to build when compiling with "--no-undefined -Wl" as ld flags

[david-geiger]

Hi,

On Mageia Linux we compile with "--no-undefined -Wl" as ld flags per default but nco fails to build with the following underlinking issue:

/usr/bin/ld: /home/david/mgarepo/03_Plasma/nco/BUILD/nco-5.1.6/src/nco/nco_cln_utl.c:689: undefined reference to `nco_prg_nm_get'

Attached full build log:
log.nco.txt

[czender]

NCO defines some one-liner functions that access global variables, like nco_prg_nm_get(), in a part of the nco.h header only visible to source files that include main(), e.g., ncks.c. Thus the library contains only the function prototype, not the function definition. We would need a PR to refactor the nco.h header, and probably all the source files that contain main(), in order for --no-undefined -Wl to succeed. I was never sure of the best way to handle access to global variables by the library. Hopefully a volunteer will figure out a solution that is still moderately elegant and avoids redundant code.