This patch adds support for .preinit_array, .init_array and .fini_array

This patch adds support for .preinit_array, .init_array and .fini_array
to the elf2flt linker script.  This seems useful in itself, and is
actually required for recent versions of uclibc, where UCLIBC_CTOR_DTOR=y
depends on the associated array symbols being defined.

Tested on m68k-uclinux using the gcc and g++ DejaGNU testsuites.  I also
ran some tests by hand to make sure that callbacks in the array sections
were being called at the right time.  Please install if OK.

Richard

Signed-off-by: Richard Sandiford <richard@codesourcery.com>