Add a COMMENT describing what each component roughly does.

"make describe" prints the comment.

Requested/inspired by Vincent Schwarzer on rumpkernel-users

Globally define -Wno-pointer-sign, as it has become a pointless
exercise of "add it to every Makefile individually".

XXX: should autosynchronize with the rest of the kernel buildflags
in sys/conf/Ma

Globally define -Wno-pointer-sign, as it has become a pointless
exercise of "add it to every Makefile individually".

XXX: should autosynchronize with the rest of the kernel buildflags
in sys/conf/Makefile.kern.inc.

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Maintain consistency of naming between the rumpfs library name and
the MOUNT_FOOFS name. Don't bother polluting the obsolete lists
with the original names since they were in only for a few days.