Add support for ashmem-host for host Windows

Migrate to tmpfile and fileno for temp file operations. These calls are
supported on MinGW, and the temp files are automatically cleaned up.

A Windows variant of ashmem-host is needed to support CursorWindows on
host Windows.

In Windows, it is not possible to unlink an open file, so the nlink
check in ashmem_validate_stat must be made Unix-only.

Test: SQLiteDatabaseTest in Google3
Test: libcutils_test_static on Windows

Bug: 317884162
Change-Id: I7fc0f1f49406b01549b7f4d7e138cb3e4d79be72