Discard .comment and .note sections when linking

When not mentioned in the linker script, these sections can be inserted
by default and may be placed before _start, with ".note.gnu.build-id" in
particular being problematic.  Since these sections are metadata inserted
by the compiler/linker toolchain and have no standard meaning, there is
currently no compelling reason to keep them around.

This commit changes this on all platforms, since ELF is architecture
independent and this problem probably can show up on any architecture.

Suggested-by: John Sullivan <jsgthb@kanargh.force9.co.uk>