Silence a new MSVC warning

This silences the following warnings in MSVC 2026 18.0 (and
2022 17.14):

    ../tools/dav1d_cli_parse.c(213): warning C5287: operands are different enum types 'CpuFlags' and 'CpuMask'; use an explicit cast to silence this warning
    ../tools/dav1d_cli_parse.c(214): warning C5287: operands are different enum types 'CpuFlags' and 'CpuMask'; use an explicit cast to silence this warning
    ../tools/dav1d_cli_parse.c(215): warning C5287: operands are different enum types 'CpuFlags' and 'CpuMask'; use an explicit cast to silence this warning
    ../tools/dav1d_cli_parse.c(216): warning C5287: operands are different enum types 'CpuFlags' and 'CpuMask'; use an explicit cast to silence this warning

This warning flag was new in MSVC 2022 17.14, but it was buggy
in that version - it produced spurious warnings for other cases
as well (and using an explicit cast to silence it didn't work
as advertised), see [1] and [2].

The bugs were fixed in 18.0, and the remaining construct that it
warns about is something that is somewhat reasonable to warn about:

    enum CpuFlags {
        DAV1D_X86_CPU_FLAG_SSE2        = 1 << 0,
        DAV1D_X86_CPU_FLAG_SSSE3       = 1 << 1,
    };
    enum CpuMask {
        X86_CPU_MASK_SSE2      = DAV1D_X86_CPU_FLAG_SSE2,
        X86_CPU_MASK_SSSE3     = DAV1D_X86_CPU_FLAG_SSSE3     | X86_CPU_MASK_SSE2,
    };

Instead of adding explicit casts on the constants from the foreign
enum, just disable this warning.

[1] https://developercommunity.visualstudio.com/t/False-positive-C5287:-operands-are-diff/10915265
[2] https://developercommunity.visualstudio.com/t/warning-C5287:-operands-are-different-e/10877942

meson.build

@@ -299,7 +299,8 @@ else
     optional_arguments += [
       '-wd4028', # parameter different from declaration
       '-wd4090', # broken with arrays of pointers
-      '-wd4996'  # use of POSIX functions
+      '-wd4996', # use of POSIX functions
+      '-wd5287', # operands are different enum types
     ]
 endif