Windows: Prevent LOG handle from being inherited by subprocesses

[dktapps]

I recently encountered a problem with this because Windows doesn't allow
files to be deleted when there's open handles to them.

Other files opened by leveldb are not affected because by and large they
are using CreateFileA, which does not allow inheritance when
lpSecurityAttributes is null (ref:
https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea)

However, fopen() does allow inheritance, and it needs to be expressly
disabled.
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/fopen-wfopen?view=msvc-160

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[dktapps]

@googlebot I signed it!

[pwnall]

LGTM. Thank you for your contribution!

"N" is not standardized (POSIX, C2011, etc.) but it is documented in MSDN: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/fopen-wfopen?view=msvc-170 -- I think this is sufficient for Windows-specific code.

This PR will get imported in our internal repository, and then a bot will merge it here.

[dktapps]

Awesome, thanks.