Fix the build of the Python bindings.

[robquill]

When attempting the build the Python bindings like this:

cmake -DKOMPUTE_OPT_BUILD_PYTHON=ON ..
make

I get this error:

[100%] Linking CXX shared module ../lib/kp.cpython-310-x86_64-linux-gnu.so
lto-wrapper: warning: using serial compilation of 2 LTRANS jobs
/usr/bin/ld: ../lib/libfmt.a(format.cc.o): warning: relocation against `stdout@@GLIBC_2.2.5' in read-only section `.text'
/usr/bin/ld: ../lib/libkompute.a(Algorithm.cpp.o): relocation R_X86_64_PC32 against symbol `_ZTINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
make[2]: *** [python/CMakeFiles/kp.dir/build.make:102: lib/kp.cpython-310-x86_64-linux-gnu.so] Error 1
make[1]: *** [CMakeFiles/Makefile2:373: python/CMakeFiles/kp.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

[axsaucedo]

Thank you for the contribution @robquill - this could make sense, but could you expand what this flag would do in context of the broader codebase? Asking as if it's more of a corner case for a particular use-case, it may make more sense adding this on the respective project cmake file as opposed to by default to the repo to all targets

[robquill]

My understanding is that building a shared object requires position-independent code (https://stackoverflow.com/questions/57649452/why-must-shared-libraries-be-position-independent-while-static-libraries-dont), so I could try only setting this option if -DKOMPUTE_OPT_BUILD_PYTHON=ON is set.

I don't think you can only set it e.g. for the Pybind11 module itself as that shared library is still built using the static libraries which would still contain position dependent code.

[axsaucedo]

so I could try only setting this option if -DKOMPUTE_OPT_BUILD_PYTHON=ON is set

From my understanding position independent code is glowingly the default in more modern distros, and it may indeed be the case that restricting it to only -DKOMPUTE_OPT_BUILD_PYTHON=ON may be the way to go, as I can't think of a corner case at this stage (unless someone wants to build static vs dynamic version of python although haven't tried if possible)

[robquill]

so I could try only setting this option if -DKOMPUTE_OPT_BUILD_PYTHON=ON is set

From my understanding position independent code is glowingly the default in more modern distros, and it may indeed be the case that restricting it to only -DKOMPUTE_OPT_BUILD_PYTHON=ON may be the way to go, as I can't think of a corner case at this stage (unless someone wants to build static vs dynamic version of python although haven't tried if possible)

OK then, that is already done, so I think this should be good to go.