Three copies of the linuxulator linux_sysvec.c contained identical BSD to Linux errno translation tables, and future work to support other architectures will also use the same table. Move the table to a common file to be used by all. Make it 'const int' to place it in .rodata.
(Some existing Linux architectures use MD errno values, but x86 and Arm share the generic set.)
This change should introduce no functional change; a followup will add missing errno values.
Sponsored by: Turing Robotic Industries Inc.