Create kernel32_vista_static library and link both kernel32_vista and kernel32 to it.
Export some vista functions from kernel32.
Export BaseProcessInitPostImport for Vista+, too, because ntdll needs to dynamically link to it.
Get rid of BaseThreadStartupThunk and BaseProcessStartThunk asm wrappers and go to the C functions directly (home space is allocated on the stack by the kernel)
There is no need to compile our DLLs as shared libraries since we are
managing symbols exports and imports through spec files.
On my system, this reduces the configure-time by a factor of two.