We need to select which SIMD variable to check based on the compilation
target: HAVE_KERNEL_xxx for the Linux kernel, HAVE_TOOLCHAIN_xxx for
other platforms.
This adds a HAVE_SIMD() macro returns the right result depending on the
definedness or value of the variable for this target.
The macro is in simd_config.h, which is forcibly included in every
compiler call (like zfs_config.h), to ensure that it can be used
directly without further includes.
Sponsored-by: TrueNAS
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@truenas.com>
Closes#18285
