Tests fail to build on 32-bit systems

[QuLogic]

I'm not sure if you still support 32-bit systems, but as of 9d16bf5 (which added -Werror), some tests don't compile:

FAILED: [code=1] test/CMakeFiles/test_xbasic_fixed_string.dir/test_xbasic_fixed_string.cpp.o 
/usr/bin/g++ -DHAVE_NLOHMANN_JSON -I/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m32 -march=i686 -mtune=generic -msse2 -mfpmath=sse -mstackrealign -fasynchronous-unwind-tables -fstack-clash-protection -mtls-dialect=gnu -DNDEBUG -Werror -Wall -Wextra -Wconversion -Wsign-conversion -MD -MT test/CMakeFiles/test_xbasic_fixed_string.dir/test_xbasic_fixed_string.cpp.o -MF test/CMakeFiles/test_xbasic_fixed_string.dir/test_xbasic_fixed_string.cpp.o.d -o test/CMakeFiles/test_xbasic_fixed_string.dir/test_xbasic_fixed_string.cpp.o -c /builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/test/test_xbasic_fixed_string.cpp
In file included from /builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xbasic_fixed_string.hpp:28,
                 from /builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/test/test_xbasic_fixed_string.cpp:10:
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp: In function ‘uint64_t xtl::murmur2_x64(const void*, std::size_t, uint64_t)’:
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp:204:55: error: conversion from ‘uint64_t’ {aka ‘long long unsigned int’} to ‘std::size_t’ {aka ‘unsigned int’} may change value [-Werror=conversion]
  204 |         return detail::murmur_hash<8>(buffer, length, seed);
      |                                                       ^~~~
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp: In function ‘uint32_t xtl::detail::murmur2_x86_impl(const void*, std::size_t, uint32_t)’:
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp:75:23: error: this statement may fall through [-Werror=implicit-fallthrough=]
   75 |             case 3: h ^= static_cast<uint32_t>(data[2] << 16);
      |                     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp:76:13: note: here
   76 |             case 2: h ^= static_cast<uint32_t>(data[1] << 8);
      |             ^~~~
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp:76:23: error: this statement may fall through [-Werror=implicit-fallthrough=]
   76 |             case 2: h ^= static_cast<uint32_t>(data[1] << 8);
      |                     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/builddir/build/BUILD/xtl-0.8.2-build/xtl-0.8.2/include/xtl/xhash.hpp:77:13: note: here
   77 |             case 1: h ^= static_cast<uint32_t>(data[0]);
      |             ^~~~
cc1plus: all warnings being treated as errors