When building world with ccache some files require closing stdin to complete:

===> lib/libc (obj,depend,all,install)
install -C -o root -g wheel -m 444  crtbegin.o /usr/obj/usr/src/tmp/usr/lib/crtbegin.o
install -C -o root -g wheel  -m 444 crti.o crtn.o gcrt1.o crt1.o Scrt1.o /usr/obj/usr/src/tmp/usr/lib
install -C -o root -g wheel -m 444  crtend.o /usr/obj/usr/src/tmp/usr/lib/crtend.o
install -C -o root -g wheel -m 444  crtbeginT.o /usr/obj/usr/src/tmp/usr/lib/crtbeginT.o
install -C -o root -g wheel -m 444  crtbegin.So /usr/obj/usr/src/tmp/usr/lib/crtbeginS.o
install -C -o root -g wheel -m 444  crtend.So /usr/obj/usr/src/tmp/usr/lib/crtendS.o
/usr/local/libexec/ccache/world-cc -fpic -DPIC -O2 -pipe -march=athlon-xp -I/usr/src/lib/libc/include -I/usr/src/lib/libc/../../include -I/usr/src/lib/libc/i386 -DNLS -D__DBINTERFACE_PRIVATE -I/usr/src/lib/libc/../../contrib/gdtoa -DINET6 -I/usr/obj/usr/src/lib/libc -I/usr/src/lib/libc/resolv -D_ACL_PRIVATE -DPOSIX_MISTAKE -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN -I/usr/src/lib/libc/rpc -DYP -DHESIOD -DNS_CACHING -DSYMBOL_VERSIONING -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-pointer-sign -c nslexer.c -o nslexer.So
/usr/local/libexec/ccache/world-cc -O2 -pipe -march=athlon-xp -I/usr/src/lib/libc/include -I/usr/src/lib/libc/../../include -I/usr/src/lib/libc/i386 -DNLS -D__DBINTERFACE_PRIVATE -I/usr/src/lib/libc/../../contrib/gdtoa -DINET6 -I/usr/obj/usr/src/lib/libc -I/usr/src/lib/libc/resolv -D_ACL_PRIVATE -DPOSIX_MISTAKE -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN -I/usr/src/lib/libc/rpc -DYP -DHESIOD -DNS_CACHING -DSYMBOL_VERSIONING -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-pointer-sign -c nslexer.c
load: 2.52  cmd: ccache 31292 [piperd] 29.02r 0.01u 0.00s 0% 1184k
load: 0.91  cmd: ccache 31292 [piperd] 98.61r 0.01u 0.00s 0% 1184k
^C
# cd /usr/obj/usr/src/lib/libc
# /usr/local/libexec/ccache/world-cc -O2 -pipe -march=athlon-xp -I/usr/src/lib/libc/include -I/usr/src/lib/libc/../../include -I/usr/src/lib/libc/i386 -DNLS -D__DBINTERFACE_PRIVATE -I/usr/src/lib/libc/../../contrib/gdtoa -DINET6 -I/usr/obj/usr/src/lib/libc -I/usr/src/lib/libc/resolv -D_ACL_PRIVATE -DPOSIX_MISTAKE -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN -I/usr/src/lib/libc/rpc -DYP -DHESIOD -DNS_CACHING -DSYMBOL_VERSIONING -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-pointer-sign -c nslexer.c
load: 0.07  cmd: ccache 31357 [ttyin] 1.32r 0.01u 0.00s 0% 1188k
load: 0.07  cmd: ccache 31357 [ttyin] 1.60r 0.01u 0.00s 0% 1188k
load: 0.07  cmd: ccache 31357 [ttyin] 1.86r 0.01u 0.00s 0% 1188k
load: 0.07  cmd: ccache 31357 [ttyin] 2.10r 0.01u 0.00s 0% 1188k
load: 0.07  cmd: ccache 31357 [ttyin] 2.35r 0.01u 0.00s 0% 1188k
load: 0.07  cmd: ccache 31357 [ttyin] 2.61r 0.01u 0.00s 0% 1188k
^C
# /usr/local/libexec/ccache/world-cc -O2 -pipe -march=athlon-xp -I/usr/src/lib/libc/include -I/usr/src/lib/libc/../../include -I/usr/src/lib/libc/i386 -DNLS -D__DBINTERFACE_PRIVATE -I/usr/src/lib/libc/../../contrib/gdtoa -DINET6 -I/usr/obj/usr/src/lib/libc -I/usr/src/lib/libc/resolv -D_ACL_PRIVATE -DPOSIX_MISTAKE -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN -I/usr/src/lib/libc/rpc -DYP -DHESIOD -DNS_CACHING -DSYMBOL_VERSIONING -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-pointer-sign -c nslexer.c
^D

After building both nslexer.c this way I can resume buildworld (with NO_CLEAN of course).

How-To-Repeat: Tiny snippet from my make.conf.

.if (empty(.CURDIR:N*/usr/src/*) || empty(.CURDIR:N*/usr/obj/*)) && !defined(NOCCACHE)
  CC=/usr/local/libexec/ccache/world-cc
  CXX=/usr/local/libexec/ccache/world-c++
.endif