ahci: enable simple test on x86_64

Related to #1133.
fixup: "vbox: join emt and vcpu handler thread"
fixup: "libc: don't take alien thread for main pthread"
fixup "vmm: parameterize Vcpu_dispatcher"
libc: move mem alloc definition in header file

Prerequisite to fix Issue #1130, to be able to reinstantiate the libc
memory allocator several times if wanted.
vbox: use separate memory spaces

Use the libc Mem_alloc implementation per MMTYP of virtualbox. With this the
invariant that all memory allocation of a MMTYP are dense located.

Fixes #1130