* libnosys/warning.h (link_warning) [HAVE_GNU_LD and HAVE_ELF]:
Prefix symbol in section name with __SYMBOL_PREFIX. Do not use
__make_section_unallocated. Mark magic variable as used.
* libnosys/warning.h (__make_section_unallocated)
[HAVE_ASM_PREVIOUS_DIRECTIVE, HAVE_ASM_POPSECTION_DIRECTIVE]: Use "\n"
instead of ";" to delimit assembly lines.
* libnosys/configure.in: Check gcc's support for section attributes.
* libnosys/warning.h: Have link_warning expand to nothing if gcc
does not support section attributes.
