libelf: move include of <asm/guest_access.h> to top of file

libelf: move include of <asm/guest_access.h> to top of file

libelf-loader.c #includes <asm/guest_access.h>, when being compiled
for Xen.  Currently it does this in the middle of the file.

Move this #include to the top of the file, before libelf-private.h.
This is necessary because in forthcoming patches we will introduce
private #defines of memcpy etc. which would interfere with definitions
in headers #included from guest_access.h.

No semantic or functional change in this patch.

This is part of the fix to a security issue, XSA-55.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Chuck Anderson <chuck.anderson@oracle.com>