duckstation: build with clang

Fails to build with gcc:

duckstation> In function 'void* memcpy(void*, const void*, size_t)',
duckstation>     inlined from 'FileSystem::AtomicRenamedFile
FileSystem::CreateAtomicRenamedFile(std::string, const char*, Error*)'
at /build/source/src/common/file_system.cpp:1213:16:
duckstation>
/nix/store/wlavaybjbzgllhq11lib6qgr7rm8imgp-glibc-2.39-52-dev/include/bits/string_fortified.h:29:33:
warning: 'void* __builtin___memcpy_chk(void*, const void*, long unsigned
int, long unsigned int)' accessing 9223372036854775801 or more bytes at
offsets 0 and 0 overlaps 9223372036854775795 bytes at offset 6
[-Wrestrict]

Warnings before building:

duckstation>   *************** UNSUPPORTED CONFIGURATION ***************
duckstation>
duckstation>   You are not compiling DuckStation with a supported
compiler.
duckstation>
duckstation>   It may not even build successfully.
duckstation>
duckstation>   DuckStation only supports the Clang and MSVC compilers.
duckstation>
duckstation>   No support will be provided, continue at your own risk.
duckstation>
duckstation>   *********************************************************

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