linux: Add version 6.18.15

[donald]

No description provided.

[donald]

nvidia_linux doesn't build:

 CONFTEST: drm_alpha_blending_available
 CONFTEST: is_export_symbol_present_drm_gem_prime_fd_to_handle
 CONFTEST: is_export_symbol_present_drm_gem_prime_handle_to_fd
 CONFTEST: ib_peer_memory_symbols
  CC [M]  nvidia/nv.o
nvidia/nv.c:30:10: fatal error: nv-firmware.h: No such file or directory
   30 | #include "nv-firmware.h"
      |          ^~~~~~~~~~~~~~~
compilation terminated.
make[4]: *** [/scratch/local/linux-6.18.15-490.x86_64/source/scripts/Makefile.build:287: nvidia/nv.o] Error 1
make[3]: *** [/scratch/local/linux-6.18.15-490.x86_64/source/Makefile:2020: .] Error 2
make[2]: *** [/scratch/local/linux-6.18.15-490.x86_64/source/Makefile:248: __sub-make] Error 2
make[2]: Leaving directory '/scratch/local/bee-buczek/nvidia/nvidia_linux-6.18.15-490-570.144-0/source/kernel'
make[1]: *** [Makefile:248: __sub-make] Error 2
make[1]: Leaving directory '/scratch/local/linux-6.18.15-490.x86_64/source'
make: *** [Makefile:115: modules] Error 2