busybox: fix stage0 build

another regression of 2fb00b74b362ac6d0b3f1ef5dfe36ec865fecc2e

$CC in stage0 works only with -static, since otherwise libc.so can't
be found.
fix utils/resume-stage0

regression from ca23b8f95ccf1c4756df8c4417e1078c0d53d220
make /var/tmp a symlink to /tmp

fixes #98