Problem building 6.0b5 on 4.11

I'm trying to migrate my 4.11 box up to 6.0b5 via source, using both
the migration doc for 5.x, as well as UPDATING from 6 to try and catch
any potential gotchas.

mergemaster -p goes through fine

I nuked the old g++ headers as directed

I then tried to do a make buildworld and this is where I hit trouble

The first thing it wants to do is update make, I get the following
when it tries:

cyrix-dlc# env -i make buildworld

--------------------------------------------------------------
>>> Building an up-to-date make(1)
--------------------------------------------------------------
rm -f .depend
mkdep -f
.depend -a    -I/usr/src/usr.bin/make -DMAKE_VERSION=\"5200408120\" -D__FBSDID=__RCSID
 -DDEFSHELLNAME=\"sh\"  /usr/src/usr.bin/make/arch.c
/usr/src/usr.bin/make/buf.c /usr/src/usr.bin/make/cond.c
/usr/src/usr.bin/make/dir.c /usr/src/usr.bin/make/for.c
/usr/src/usr.bin/make/hash.c /usr/src/usr.bin/make/hash_tables.c
/usr/src/usr.bin/make/job.c /usr/src/usr.bin/make/lst.c
/usr/src/usr.bin/make/main.c /usr/src/usr.bin/make/make.c
/usr/src/usr.bin/make/parse.c /usr/src/usr.bin/make/proc.c
/usr/src/usr.bin/make/shell.c /usr/src/usr.bin/make/str.c
/usr/src/usr.bin/make/suff.c /usr/src/usr.bin/make/targ.c
/usr/src/usr.bin/make/util.c /usr/src/usr.bin/make/var.c
In file included from /usr/src/usr.bin/make/arch.c:107:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/cond.c:59:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/dir.c:97:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/for.c:55:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/job.c:131:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/main.c:84:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/make.c:80:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/parse.c:86:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/str.c:49:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/suff.c:102:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/targ.c:84:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/util.c:59:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
In file included from /usr/src/usr.bin/make/var.c:96:
/usr/src/usr.bin/make/globals.h:49: stdint.h: No such file or
directory
mkdep: compile failed
*** Error code 1

Stop in /usr/src/usr.bin/make.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
cyrix-dlc# locate stdint.h
/usr/local/include/zzip/stdint.h
/usr/src/sys/alpha/include/_stdint.h
/usr/src/sys/amd64/include/_stdint.h
/usr/src/sys/arm/include/_stdint.h
/usr/src/sys/i386/include/_stdint.h
/usr/src/sys/ia64/include/_stdint.h
/usr/src/sys/pc98/include/_stdint.h
/usr/src/sys/powerpc/include/_stdint.h
/usr/src/sys/sparc64/include/_stdint.h
/usr/src/sys/sys/stdint.h

I checked, and I don't see anything about updating my base includes,
and I would think the buildworld system would default to using the src
includes, not the system's.

Suggestions on how to proceed?

Joshua Coombs