dev-libs/msgpack-1.2.0 fails to build

[chrboe]

msgpack fails to compile with the following error:

In file included from /var/tmp/portage/dev-libs/msgpack-1.2.0/work/msgpack-1.2.0/src/unpack.c:276:0:
/var/tmp/portage/dev-libs/msgpack-1.2.0/work/msgpack-1.2.0/include/msgpack/unpack_template.h: In function 'template_execute':
/var/tmp/portage/dev-libs/msgpack-1.2.0/work/msgpack-1.2.0/include/msgpack/unpack_template.h:258:17: error: this statement may fall through [-Werror=implicit-fallthrough=]
                 ++p;
                 ^~~
/var/tmp/portage/dev-libs/msgpack-1.2.0/work/msgpack-1.2.0/include/msgpack/unpack_template.h:260:13: note: here
             default:
             ^~~~~~~

My system:

$ uname -srop
Linux 4.16.0+ Intel(R) Core(TM) i7-3667U CPU @ 2.00GHz GNU/Linux

$ gcc -v
Using built-in specs.
COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/7.2.0/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/7.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/notmpfs/portage/sys-devel/gcc-7.2.0-r1/work/gcc-7.2.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/7.2.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.2.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.2.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/7.2.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/include/g++-v7 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/7.2.0/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --disable-nls --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 7.2.0-r1 p1.1' --disable-esp --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64 --disable-altivec --disable-fixed-point --enable-targets=all --disable-libgcj --enable-libgomp --disable-libmudflap --disable-libssp --disable-libcilkrts --disable-libmpx --enable-vtable-verify --enable-libvtv --enable-lto --without-isl --enable-libsanitizer --enable-default-pie --enable-default-ssp
Thread model: posix
gcc version 7.2.0 (Gentoo 7.2.0-r1 p1.1)

$ emerge -pqv dev-libs/msgpack
[ebuild     U ] dev-libs/msgpack-1.2.0 [1.1.0] USE="cxx -static-libs {-test}" ABI_X86="32 (64) (-x32)"