Update Makefile of ReLAPACK

[amontoison]

We need this modification if we want to compile ReLAPACK and also not override the .o and symbols generated by LAPACK (INCLUDE_ALL=0 in relapack/config.h).

[martin-frbg]

Ahem, wouldn't that break the default build by enforcing relapack prefixes even when not desired ?

[amontoison]

You're right @martin-frbg, we should only add a prefix if INCLUDE_ALL=0 in relapack/config.h.
If we have two .o with different names but the same exported symbols, the library will use the routines of the first .o file added in the library.

Do you have an idea how can check the value of INCLUDE_ALL from relapack/Makefile?
We could also just define RELAPACK_PREFIX in the same spirit of SUFFIX in the relapack/Makefile for more flexibility.

[martin-frbg]

It would probably make sense to have tighter integration with the OpenBLAS makefiles, i.e. moving the INCLUDE_ALL from config.h to a RELAPACK_INCLUDEALL in Makefile.rule (so that one does not have to hack around in the ReLAPACK internals) and then having the ReLAPACK makefile add -DINCLUDE_ALL=$RELAPACK_INCLUDEALL to the %.o: %.c build rule.
(Plus the equivalent for the cmake build system)

[amontoison]

I saw that you opened #3796 and #3802, should I close this PR?

[martin-frbg]

Sorry, I did not intend to deny you recognition but the changes got a bit out of hand, what with the preexisting bugs in the cmake files and the need to integrate with the hackish GEMMT I already had lying around

[amontoison]

It's perfectly fine @martin-frbg! I don't know well CMake.
I also didn't know if I should update the symbols or RELAPACK in OpenBLAS/exports folder.