Compile time assertion failure

[Bruno Wolff III <bruno@wolff.to>]

I'm seeing the following:

[bruno@wolff src]$ make clean all
make -C /lib/modules/4.13.0-0.rc3.git0.1.fc27.i686+PAE/build M=/home/bruno/WireGuard/src clean
make[1]: Entering directory '/usr/src/kernels/4.13.0-0.rc3.git0.1.fc27.i686+PAE'
  CLEAN   /home/bruno/WireGuard/src/.tmp_versions
  CLEAN   /home/bruno/WireGuard/src/Module.symvers
make[1]: Leaving directory '/usr/src/kernels/4.13.0-0.rc3.git0.1.fc27.i686+PAE'
make -C tools clean
make[1]: Entering directory '/home/bruno/WireGuard/src/tools'
rm -f wg *.o *.d
make[1]: Leaving directory '/home/bruno/WireGuard/src/tools'
make -C /lib/modules/4.13.0-0.rc3.git0.1.fc27.i686+PAE/build M=/home/bruno/WireGuard/src modules
make[1]: Entering directory '/usr/src/kernels/4.13.0-0.rc3.git0.1.fc27.i686+PAE'
  CC [M]  /home/bruno/WireGuard/src/main.o
  CC [M]  /home/bruno/WireGuard/src/noise.o
  CC [M]  /home/bruno/WireGuard/src/device.o
  CC [M]  /home/bruno/WireGuard/src/peer.o
  CC [M]  /home/bruno/WireGuard/src/timers.o
  CC [M]  /home/bruno/WireGuard/src/data.o
  CC [M]  /home/bruno/WireGuard/src/send.o
  CC [M]  /home/bruno/WireGuard/src/receive.o
  CC [M]  /home/bruno/WireGuard/src/socket.o
  CC [M]  /home/bruno/WireGuard/src/config.o
  CC [M]  /home/bruno/WireGuard/src/hashtables.o
  CC [M]  /home/bruno/WireGuard/src/routingtable.o
In file included from ./include/uapi/linux/stddef.h:1:0,
                 from ./include/linux/stddef.h:4,
                 from ./include/uapi/linux/posix_types.h:4,
                 from ./include/uapi/linux/types.h:13,
                 from ./include/linux/types.h:5,
                 from /home/bruno/WireGuard/src/compat/compat.h:8,
                 from <command-line>:0:
In function ‘common_bits’,
    inlined from ‘node_placement.constprop’ at /home/bruno/WireGuard/src/routingtable.c:170:39,
    inlined from ‘add.part.1’ at /home/bruno/WireGuard/src/routingtable.c:195:6:
./include/linux/compiler.h:542:38: error: call to ‘__compiletime_assert_129’ declared with attribute error: BUILD_BUG_ON failed: !__builtin_constant_p(bits) || (bits != 32 && bits != 128)
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:525:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:542:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:46:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:70:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  ^~~~~~~~~~~~~~~~
/home/bruno/WireGuard/src/routingtable.c:129:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(!__builtin_constant_p(bits) || (bits != 32 && bits != 128));
  ^~~~~~~~~~~~
In function ‘common_bits’,
    inlined from ‘add.part.1’ at /home/bruno/WireGuard/src/routingtable.c:215:9:
./include/linux/compiler.h:542:38: error: call to ‘__compiletime_assert_129’ declared with attribute error: BUILD_BUG_ON failed: !__builtin_constant_p(bits) || (bits != 32 && bits != 128)
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:525:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:542:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:46:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:70:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  ^~~~~~~~~~~~~~~~
/home/bruno/WireGuard/src/routingtable.c:129:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(!__builtin_constant_p(bits) || (bits != 32 && bits != 128));
  ^~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:303: /home/bruno/WireGuard/src/routingtable.o] Error 1
make[1]: *** [Makefile:1515: _module_/home/bruno/WireGuard/src] Error 2
make[1]: Leaving directory '/usr/src/kernels/4.13.0-0.rc3.git0.1.fc27.i686+PAE'
make: *** [Makefile:28: module] Error 2