undefined reference to `pps_unregister_source'

[kbuild test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   238d1d0f79f619d75c2cc741d6770fb0986aef24
commit: ee84595a91c60d33cbf1d5b941b04a3ee6cf7ce0 afs, rxrpc: Update the MAINTAINERS file
date:   2 weeks ago
config: x86_64-randconfig-s1-01012230 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        git checkout ee84595a91c60d33cbf1d5b941b04a3ee6cf7ce0
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   drivers/built-in.o: In function `ptp_clock_unregister':
>> (.text+0x40e0a5): undefined reference to `pps_unregister_source'
   drivers/built-in.o: In function `ptp_clock_unregister':
>> (.text+0x40e0cc): undefined reference to `posix_clock_unregister'
   drivers/built-in.o: In function `ptp_clock_event':
>> (.text+0x40e249): undefined reference to `pps_event'
   drivers/built-in.o: In function `ptp_clock_register':
>> (.text+0x40e5e1): undefined reference to `pps_register_source'
   drivers/built-in.o: In function `ptp_clock_register':
>> (.text+0x40e62c): undefined reference to `posix_clock_register'
   drivers/built-in.o: In function `ptp_clock_register':
   (.text+0x40e68d): undefined reference to `pps_unregister_source'

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