Description of problem:
fmt does not build on f26 with gcc-6.2.1:

[ 47%] Building CXX object test/CMakeFiles/posix-mock-test.dir/util.cc.o
cd /builddir/build/BUILD/fmt-3.0.0/build/test && /usr/bin/c++   -DFMT_USE_FILE_DESCRIPTORS=1 -DGTEST_HAS_STD_WSTRING=1 -I/builddir/build/BUILD/fmt-3.0.0 -I/builddir/build/BUILD/fmt-3.0.0/test/.  -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -mtune=generic -DNDEBUG   -std=c++11 -o CMakeFiles/posix-mock-test.dir/util.cc.o -c /builddir/build/BUILD/fmt-3.0.0/test/util.cc
In file included from /usr/lib/gcc/x86_64-redhat-linux/6.2.1/include/limits.h:168:0,
                 from /usr/lib/gcc/x86_64-redhat-linux/6.2.1/include/syslimits.h:7,
                 from /usr/lib/gcc/x86_64-redhat-linux/6.2.1/include/limits.h:34,
                 from /builddir/build/BUILD/fmt-3.0.0/test/./gmock/gmock.h:2028,
                 from /builddir/build/BUILD/fmt-3.0.0/test/gtest-extra.h:32,
                 from /builddir/build/BUILD/fmt-3.0.0/test/gtest-extra.cc:28:
/builddir/build/BUILD/fmt-3.0.0/fmt/format.h: In member function 'void fmt::internal::ArgFormatterBase<Impl, Char>::visit_char(int)':
/builddir/build/BUILD/fmt-3.0.0/fmt/format.h:1825:20: error: expected unqualified-id before numeric constant
     const unsigned CHAR_WIDTH = 1;
                    ^

Version-Release number of selected component (if applicable):
fmt-3.0.0

How reproducible:
Rebuild on f26 with gcc-6.2.1

Build log: https://copr-be.cloud.fedoraproject.org/results/sagitter/petsc/fedora-rawhide-x86_64/00465843-fmt/build.log.gz

Root log: https://copr-be.cloud.fedoraproject.org/results/sagitter/petsc/fedora-rawhide-x86_64/00465843-fmt/root.log.gz