[boost-math] build failure x64-linux-dynamic

[Allen Winter]

Operating system

linux

Compiler

gcc-13

Steps to reproduce the behavior

I have lots of boost packages listed in a vcpkg.json and using that to build a project in manifest-mode

        "boost-asio",
        "boost-container",
        "boost-system",
        "boost-thread",
        "boost-filesystem",
        "boost-graph",
        "boost-geometry",
        {
            "name": "boost-iostreams",
            "default-features": false,
            "features": [
                "bzip2",
                "zlib",
                "zstd"
            ]
        },
        "boost-multi-array",
        "boost-polygon",
        "boost-unordered",
        "boost-uuid",
        "boost-interprocess",
        {
            "name": "curl",
            "platform": "windows"
        },

Failure logs

the compile fails with

/home/build/vcpkg/buildtrees/boost-math/src/ost-1.85.0-7b137ed96b.clean/libs/math/include/boost/math/special_functions/next.hpp:697:56: error: expected ‘;’ before ‘{’ token
  697 |    BOOST_MATH_IF_CONSTEXPR (!std::is_same<T, U>::value)
      |                                                        ^
      |                                                        ;
  698 |    {
      |    ~                                                    
/home/build/cpkg/buildtrees/boost-math/src/ost-1.85.0-7b137ed96b.clean/libs/math/include/boost/math/special_functions/next.hpp:708:4: error: ‘else’ without a previous ‘if’
  708 |    else
      |    ^~~~
ninja: build stopped: subcommand failed.



### Additional context

yesterday I was trying with version 1.84 and had the same compile error.  I also tried with gcc-9 and same problem```