glsl/linker: pass through the is_intrinsic flag

glsl/linker: pass through the is_intrinsic flag

This flag was set to true for the atomic counter intrinsics, but it
never got plumbed through the linker, so by the time it got to the
backends it would always be set to the false. The current i965 backend
code doesn't use is_intrinsic, so this should not change any existing
code, but it's useful for codepaths that want to distinguish between
intrinsics and non-intrinsics without using strcmp.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Connor Abbott <connor.abbott@intel.com>