I'll second this:
root@NexGen jeff # emerge dosfstools
Calculating dependencies ...done!
>>> emerge (1 of 1) sys-fs/dosfstools-2.10 to /
>>> md5 src_uri ;-) dosfstools-2.10.src.tar.gz
>>> Unpacking source...
>>> Unpacking dosfstools-2.10.src.tar.gz to /var/tmp/portage/dosfstools-2.10/wor
k
* Applying errno.patch... [ ok ]
>>> Source unpacked.
make -C mkdosfs all
make[1]: Entering directory `/var/tmp/portage/dosfstools-2.10/work/dosfstools-2.
10/mkdosfs'
gcc -O2 -fomit-frame-pointer -Wall -c mkdosfs.c -o mkdosfs.o
gcc mkdosfs.o -o mkdosfs
make[1]: Leaving directory `/var/tmp/portage/dosfstools-2.10/work/dosfstools-2.1
0/mkdosfs'
make -C dosfsck all
make[1]: Entering directory `/var/tmp/portage/dosfstools-2.10/work/dosfstools-2.
10/dosfsck'
gcc -c -O2 -fomit-frame-pointer -Wall boot.c
boot.c: In function `read_boot':
boot.c:327: error: `MSDOS_FAT12' undeclared (first use in this function)
boot.c:327: error: (Each undeclared identifier is reported only once
boot.c:327: error: for each function it appears in.)
make[1]: *** [boot.o] Error 1
make[1]: Leaving directory `/var/tmp/portage/dosfstools-2.10/work/dosfstools-2.1
0/dosfsck'
make: *** [all] Error 2
!!! ERROR: sys-fs/dosfstools-2.10 failed.
!!! Function src_compile, Line 32, Exitcode 2
!!! (no error message)
2.6.4 headers