main/xen: fix hvmloader

hvmloader is 32 bit but pulled in 64bit stdint from musl headers. we solve
this by providing our own stdint_local.h

elf.h pulls in stdint.h too so we ship our own elf_local.h too

fixes #3308
main/xen: security fix for XSA-97 (CVE-2014-5146,CVE-2014-5149)

fixes #3294