package/grub: fix stage2 link with recent binutils

package/grub: fix stage2 link with recent binutils

We want the `_start's symbols to be at the very beginning of the `stage2'
binary's `.text' section. However, nothing enforces this requirement. With
recent binutils (ie. post 2.19.1), this results in a corrupt binary, as ld(1)
puts another symbol (eg. `journal_init') at the beginning of the section.

Fix this by providing a stripped down version of the default linker script
where we enforces the position of `_start' in the `.text' section.

Patch by Arnaud Lacombe (#10444)

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@30484 3c298f89-4303-0410-b956-a3cf2f4a3e73