I blasted my /usr/obj today, and this was the result:

depend ===> sys/arch/sparc/stand/boot
[...]
depending the z library objects
mkdep -a -I. -D_STANDALONE -DRELOC=0x300000 -DSUN4 -DSUN4C -DSUN_BOOTPARAMS
-I/u
sr/src/sys/arch/sparc/stand/boot/../../..
-I/usr/src/sys/arch/sparc/stand/boot/.
./../../.. -nostdinc -idirafter /altroot/usr/include  -D_ZLIB_PRIVATE
-nostdinc
-idirafter /altroot/usr/include /usr/src/sys/lib/libz/adler32.c
/usr/src/sys/lib
/libz/crc32.c /usr/src/sys/lib/libz/infblock.c
/usr/src/sys/lib/libz/infcodes.c
/usr/src/sys/lib/libz/inffast.c /usr/src/sys/lib/libz/inflate.c
/usr/src/sys/lib
/libz/inftrees.c /usr/src/sys/lib/libz/infutil.c
depending the sa library objects
make: don't know how to make snprintf.c. Stop
*** Error code 2