v.kriging: Fix compilation by changing doublereal to double

[echoix]

These are similar to the changes made in the upstream repo in OSGeo/grass@d5bb442, where CBLAS was used and ATLAS dropped.

Before that commit, doublereal was typedef-ed to double, if GCC's g2c (GCC's version of f2c) was not present, in include/grass/la.h

[nilason]

It is only GRASS 8.5+ that uses the CBLAS interface. This code needs to be GRASS version aware, off the head I'm not sure what would work for Addons.

In principle something like:

#ifdef HAVE_CBLAS_H
// new code
#else
// old code
#endif

[echoix]

What about OSGeo/grass@d5bb442#diff-1df0e75a8f47991f0c38f6ff94dadf2f0d2203321bf6346136360b099ff0b086L40, where HAVE_G2C_H is used. Could #ifndef HAVE_G2C_H be appropriate?

Thinking about it again, it’s been a while since we are using gcc 4+, so we are already in the fallback where ˋtypedef double doublereal;` is used. With LLVM/clang, I suppose we were always using this.
So, is the fix of this PR really limited to GRASS 8.5+? If so, wouldn’t addons benefit of having more granular branches?

[nilason]

What about OSGeo/grass@d5bb442#diff-1df0e75a8f47991f0c38f6ff94dadf2f0d2203321bf6346136360b099ff0b086L40, where HAVE_G2C_H is used. Could #ifndef HAVE_G2C_H be appropriate?

I realised now that HAVE_CBLAS_H may have already be set also before 8.5 (not reflecting current changes in GRASS), so the version check I originally had in mind is more appropriate:

#include <grass/version.h>

#if GRASS_VERSION_MINOR >= 5
// new code
#else
// old code
#endif

Thinking about it again, it’s been a while since we are using gcc 4+, so we are already in the fallback where ˋtypedef double doublereal;` is used. With LLVM/clang, I suppose we were always using this.

If there was an issue with the previous code (pre-OSGeo/grass@d5bb442), that should be addressed separately.

So, is the fix of this PR really limited to GRASS 8.5+? If so, wouldn’t addons benefit of having more granular branches?

It would be a pain to maintain each of a minor version addos branch (if you mean a grass85 branch etc), so I'd think not.