About pkg() function and compiling options in mkoctfile

[José Luis García Pallero]

Hello:

Some days ago I asked about the reason of the -fopenmp is present by
default in mkoctfile
(https://lists.gnu.org/archive/html/octave-maintainers/2020-05/msg00057.html)

The reason of my question was that new versions of GCC handle better
than previous ones with some OpenMP directives. For example, now is
mandatory to declare explicitly all shared variables in the shared()
directive when the default(none) option is employed. Prior visions of
GCC does not require this for variables declared as const, but in the
standard was always mandatory (see
http://forum.openmp.org/forum/viewtopic.php?f=3&t=2104). So some code
must be changed in order to complain with the standard as newer GCC
versions complain. For example, the GCC provided with Debian stable
produces error when const variables are declared in shared() (see
https://sourceforge.net/p/octave/package-releases/417/#681d)

Then, the fact that mkoctfile activates by default the OpenMP support
makes some cone not compilable in some systems. I can see that the
-pthread -fopenmp options for mkoctfile are stored in the globals
ALL_CFLAGS and ALL_CXXFLAGS, which also contain some information about
include folders

But I think that ask the user to edit manually this variables in order
to install a package is not a good idea. So I propose to add an option
to the pkg() function in order to activate or deactivate the OpenMP
(and pthreads maybe) option. Or maybe more in general an option to
pass information and options from pkg() to mkoctfile. Or both things.

I think that other discussion could be if mkocfile should activate by
default the OpenMP dupport

Thanks
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José Luis García Pallero
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