WRF fails to compile with `-DNCEP_DEBUG_MULTIDIR`

[mfontanaar]

The RSL_LITE objects fail to build and, consequently, executables are not generated, when using the -DNCEP_DEBUG_MULTIDIR CFLAG. I tracked down the problem to errno not being defined, which is solved by uncommenting line 19 of external/RSL_LITE/c_code.c which reads # include <errno.h>.

I found the problem using Intel(R) Parallel Studio XE 2019 Update 1 on Linux but I'm fairly confident the same result will be obtained with other compilers and operating systems. Also, I'm using WRF v4.4, but I can see the commented line goes back a few releases, to v4.0 at least.

Is there any particular reason that line is commented? I couldn't find any information about this in the repo nor the forums.

Kind regards, Mauro Fontana