MEDIUM: sym: store a compressed symbol table in a loadable section

MEDIUM: sym: store a compressed symbol table in a loadable section

Implement the MiniDebugInfo, and store the symtab, compressed with xz,
into the .gnu_debugdata section, provided the needed utilities are
available, and we're building an ELF binary.
Makes it a loadable section, so that it is always available, and teach
haproxy to parse it, so that we will always get all available symbols
for binaries built that way, even if we can't even read the binary
itself.