Fix use-out-of-constexpr lifetime detected by prerelease MSVC

[BillyONeal]

commands.build.cpp

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\src\vcpkg\commands.build.cpp(1498,68): error C7595: 'fmt::v10::basic_format_string<char,const std::string &>::basic_format_string': call to immediate function is not a constant expression

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\include\vcpkg\base\stringview.h(33,62): note: failure was caused by a read of a variable outside its lifetime

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\include\vcpkg\base\stringview.h(33,62): note: see usage of 'details_start'

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\src\vcpkg\commands.build.cpp(1498,68): note: the call stack of the evaluation (the oldest call first) is

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\src\vcpkg\commands.build.cpp(1498,68): note: while evaluating function 'const char *vcpkg::ZStringView::c_str(void) noexcept const'

E:\Repro\RWC\vcpkg_tool_repro\vcpkg-tool\include\vcpkg\base\stringview.h(85,67): note: while evaluating function 'const char *vcpkg::StringView::data(void) noexcept const'

This was originally reported by @Zhaojun-Liu of Beyondsoft . This fix was suggested by @joemmett of the compiler frontend team.