meson: Don't pass cpp_std=c++11 to MSVC

msvc cannot understand the compiler option.

WARNING: msvc does not support C++11; attempting best effort; setting the standard to C++14
cl : Command line warning D9002 : ignoring unknown option '/std:c++11'
29 jobs for !545 with msvc-warning in 35 minutes and 24 seconds (queued for 2 seconds)
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