build32: don't discard .shstrtab in linker script

build32: don't discard .shstrtab in linker script

LLVM linker doesn't support discarding .shstrtab, and complains with:

ld -melf_i386_fbsd -N -T build32.lds -o reloc.lnk reloc.o
ld: error: discarding .shstrtab section is not allowed

Add an explicit .shstrtab, .strtab and .symtab sections to the linker
script after the text section in order to make LLVM LD happy and match
the behavior of GNU LD.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Paul Durrant <paul@xen.org>