* Fix stdout_sink_base::log's behavior inconsistency
It will flush every time when it if not defined _WIN32, but not in
Windows family.
We viewed the commit #48d4ed9 for fixing issue #1675 .
It seems missing this flushing operation in mistake.
* Use fflush at all operating system
* Remove redundant fflush from stdout_sink_base
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Co-authored-by: scc <scc@teamt5.org>
The meaning of using quotes to #include is implementation defined, so it
may or not may be what we want. At least POSIX
(https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html)
says: "headers whose names are enclosed in double-quotes ( "" ) shall be
searched for first in the directory of the file with the #include line",
so not what we want since "spdlog" ends up twice in the path.