Looks like lsof got updated in https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195679.

On 10.1-STABLE:
===>>> lsof-4.88,8 1/1

===>>> Currently installed version: lsof-4.88,8
===>>> Port directory: /usr/ports/sysutils/lsof

===>  Cleaning for lsof-4.89.a,8
===>   lsof-4.89.a,8 depends on file: /usr/local/sbin/pkg - found
===> Fetching all distfiles required by lsof-4.89.a,8 for building
===>  Extracting for lsof-4.89.a,8
=> SHA256 Checksum OK for lsof_4.89A.freebsd.tar.bz2.
===>  Patching for lsof-4.89.a,8
===>  Configuring for lsof-4.89.a,8
Creating ./lockf_owner.h from /usr/src/sys/kern/kern_lockf.c
./lockf_owner.h creation succeeded.
rm -f ddev.c dfile.c dlsof.h dmnt.c dnode*.c dproc.c dproto.h dsock.c dstore.c dzfs.h kernelbase.h machine.h machine.h.old new_machine.h __lseek.s Makefile Makefile.zfs ./tests/config.cflags
rm -f ./tests/config.cc ./tests/config.xobj ./tests/config.ldflags
Testing C library for localtime() and strftime(), using cc ... present
ln -s dialects/freebsd/dlsof.h dlsof.h
ln -s dialects/freebsd/dmnt.c dmnt.c
ln -s dialects/freebsd/dnode.c dnode.c
ln -s dialects/freebsd/dnode1.c dnode1.c
ln -s dialects/freebsd/dnode2.c dnode2.c
ln -s dialects/freebsd/dproc.c dproc.c
ln -s dialects/freebsd/dproto.h dproto.h
ln -s dialects/freebsd/dsock.c dsock.c
ln -s dialects/freebsd/dstore.c dstore.c
ln -s dialects/freebsd/dzfs.h dzfs.h
ln -s dialects/freebsd/machine.h machine.h
Makefile and lib/Makefile created.
Makefile.zfs created.
./tests/config.cc created
./tests/config.cflags created
./tests/config.ldflags created
./tests/config.xobj created
===>  Building for lsof-4.89.a,8
Constructing version.h
(cd lib; /usr/bin/make DEBUG="-O2" CFGF="-pipe -march=pentium4 -fstack-protector -fno-strict-aliasing -march=pentium4 -DHASTASKS -DHAS_PAUSE_SBT -DHASEFFNLINK=i_effnlink -DHASF_VNODE -DHAS_FILEDESCENT -DHAS_TMPFS -DHASWCTYPE_H -DHASSBSTATE -DHAS_KVM_VNODE -DHAS_UFS1_2 -DHAS_VM_MEMATTR_T -DHAS_CDEV2PRIV -DHAS_NO_SI_UDEV -DHAS_SYS_SX_H -DHAS_ZFS -DHAS_V_LOCKF -DHAS_LOCKF_ENTRY -DHAS_NO_6PORT -DHAS_NO_6PPCB -DNEEDS_BOOLEAN_T -DFREEBSDV=10000 -DHASFDESCFS=2 -DHASPSEUDOFS -DHASNULLFS -DHASIPv6 -DHASUTMPX -DHAS_STRFTIME -DLSOF_VSTR=\"10.1-STABLE\"")
cc  -pipe -march=pentium4 -fstack-protector -fno-strict-aliasing -march=pentium4 -DHASTASKS -DHAS_PAUSE_SBT -DHASEFFNLINK=i_effnlink -DHASF_VNODE -DHAS_FILEDESCENT -DHAS_TMPFS -DHASWCTYPE_H -DHASSBSTATE -DHAS_KVM_VNODE -DHAS_UFS1_2 -DHAS_VM_MEMATTR_T -DHAS_CDEV2PRIV -DHAS_NO_SI_UDEV -DHAS_SYS_SX_H -DHAS_ZFS -DHAS_V_LOCKF -DHAS_LOCKF_ENTRY -DHAS_NO_6PORT -DHAS_NO_6PPCB -DNEEDS_BOOLEAN_T -DFREEBSDV=10000 -DHASFDESCFS=2 -DHASPSEUDOFS -DHASNULLFS -DHASIPv6 -DHASUTMPX -DHAS_STRFTIME -DLSOF_VSTR="10.1-STABLE" -I/usr/src/sys -O2 -c ckkv.c
In file included from ckkv.c:43:
In file included from ./../lsof.h:195:
In file included from ./../dlsof.h:208:
In file included from /usr/src/sys/ufs/ufs/ufsmount.h:36:
In file included from /usr/src/sys/sys/buf.h:260:
/usr/src/sys/sys/proc.h:950:1: error: unknown type name 'bool'
bool    thread_suspend_check_needed(void);
^
1 error generated.
*** [ckkv.o] Error code 1

make[2]: stopped in /usr/home/ports/sysutils/lsof/work/lsof_4.89A.freebsd/lib
1 error

make[2]: stopped in /usr/home/ports/sysutils/lsof/work/lsof_4.89A.freebsd/lib
*** [lib/liblsof.a] Error code 2

make[1]: stopped in /usr/home/ports/sysutils/lsof/work/lsof_4.89A.freebsd
1 error

make[1]: stopped in /usr/home/ports/sysutils/lsof/work/lsof_4.89A.freebsd
===> Compilation failed unexpectedly.
Try to set MAKE_JOBS_UNSAFE=yes and rebuild before reporting the failure to
the maintainer.
*** Error code 1

Stop.
make: stopped in /usr/home/ports/sysutils/lsof

===>>> make build failed for sysutils/lsof
===>>> Aborting update

===>>> Update for lsof-4.88,8 failed
===>>> Aborting update


===>>> You can restart from the point of failure with this command line:
       portmaster <flags> sysutils/lsof sysutils/tcplist ports-mgmt/packagekit

$ svn info
Path: .
Working Copy Root Path: /usr/home/ports
URL: http://svn0.us-east.freebsd.org/ports/head
Relative URL: ^/head
Repository Root: http://svn0.us-east.freebsd.org/ports
Repository UUID: 35697150-7ecd-e111-bb59-0022644237b5
Revision: 374880
Node Kind: directory
Schedule: normal
Last Changed Author: swills
Last Changed Rev: 374880
Last Changed Date: 2014-12-17 20:22:55 -0500 (Wed, 17 Dec 2014)

$ uname -a
FreeBSD static-173-53-110-7.rcmdva.fios.verizon.net 10.1-STABLE FreeBSD 10.1-STABLE #0 r275875: Thu Dec 18 05:34:32 EST 2014     root@static-173-53-110-7.rcmdva.fios.verizon.net:/usr/obj/usr/home/src/sys/STATIC-173-53-110-7  i386