boot/syslinux: fix i386 bios build with recent binutils

boot/syslinux: fix i386 bios build with recent binutils

When we use the cross-compiler to build syslinux with a recent binutils
version, it fails with:

/builds/arnout/buildroot/output/host/bin/i586-buildroot-linux-uclibc-ld  -Bsymbolic -pie -E --hash-style=gnu -T
/builds/arnout/buildroot/output/build/syslinux-6.03/core/i386/syslinux.ld -M -o ldlinux.elf ldlinux.o \
	--start-group libcom32.a --whole-archive /builds/arnout/buildroot/output/build/syslinux-6.03/bios/com32/lib/libcom32core.a libldlinux.a --end-group -N
--no-omagic \
	> ldlinux.map
/builds/arnout/buildroot/output/host/bin/i586-buildroot-linux-uclibc-ld: ldlinux.elf: Not enough room for program headers, try linking with -N
/builds/arnout/buildroot/output/host/bin/i586-buildroot-linux-uclibc-ld: final link failed: Bad value
/builds/arnout/buildroot/output/build/syslinux-6.03/core/Makefile:167: recipe for target 'ldlinux.elf' failed

Backport an upstream patch that reorganises the i386 bios build by
removing some symbols and making others hidden. To simplify the
backport, an additional patch that also touches the link script is
also included - it anyway looks like that patch could be relevant as
well.

Partially fixes: https://gitlab.com/arnout/buildroot/-/jobs/28979377

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>