[Win32, MSVC version 143] win32/perllib.c fails to compile as of perl-5.43.5 (on unthreaded builds only)

[sisyphus]

6fb21d6 (which was part of #23896) breaks unthreaded MSVC builds of perl-5.43.5.
During the compilation of perllib.c I'm getting:

perllib.c(265): error C2055: expected formal parameter list, not a type list

It looks to me that, while the affected code is "C++" for Mingw, the same is not the case for MSVC.
However, I don't know why it's only the unthreaded builds that are affected.

Do we want to make the code "C++" for MSVC, too ? (Is that a viable option ?)
Or do we want to switch to @khwilliamson's original suggestion of specifying PERL_UNUSED_ARG(lpvReserved); ?

Or maybe there's some better way.
My workaround was merely to revert perllib.c to the way it was in perl-5.43.4 - which works fine but, of course, does not silence the targeted warning.

Summary of my perl5 (revision 5 version 43 subversion 5) configuration:

  Platform:
    osname=MSWin32
    osvers=10.0.26100.7171
    archname=MSWin32-x64-perlio
    uname=''
    config_args='undef'
    hint=recommended
    useposix=true
    d_sigaction=undef
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=undef
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cl'
    ccflags ='-nologo -GF -W3 -MD -DWIN32 -D_CONSOLE -DNO_STRICT -DWIN64 -D_CRT_SECURE_NO_DEPRECATE  -D_CRT_NONSTDC_NO_DEPRECATE -D_WINSOCK_DEPRECATED_NO_WARNINGS  -DPERL_TEXTMODE_SCRIPTS'
    optimize='-O1 -Zi -GL -fp:precise'
    cppflags='-DWIN32'
    ccversion='19.33.31630'
    gccversion=''
    gccosandvers=''
    intsize=4
    longsize=4
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=undef
    longlongsize=8
    d_longdbl=define
    longdblsize=8
    longdblkind=0
    ivtype='__int64'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='__int64'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='link'
    ldflags ='-nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -libpath:"D:\perl-5.43.5-vs\lib\MSWin32-x64-perlio\CORE"  -machine:AMD64 -subsystem:console,"5.02"'
    libpth="C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.33.31629\\lib\x64" D:\_64\msys_1520_winpos\1.0\local_dyn\lib
    libs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbccp32.lib comctl32.lib msvcrt.lib vcruntime.lib ucrt.lib
    perllibs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbccp32.lib comctl32.lib msvcrt.lib vcruntime.lib ucrt.lib
    libc=ucrt.lib
    so=dll
    useshrplib=true
    libperl=perl543.lib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_win32.xs
    dlext=dll
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags='-dll -nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -libpath:"D:\perl-5.43.5-vs\lib\MSWin32-x64-perlio\CORE"  -machine:AMD64 -subsystem:console,"5.02"'


Characteristics of this binary (from libperl):
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_TIMES
    HAVE_INTERP_INTERN
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under MSWin32
  Compiled at Nov 21 2025 11:19:17
  @INC:
    D:/perl-5.43.5-vs/site/lib/MSWin32-x64-perlio
    D:/perl-5.43.5-vs/site/lib
    D:/perl-5.43.5-vs/lib/MSWin32-x64-perlio
    D:/perl-5.43.5-vs/lib