For Windows, make sure the file handle created by os::fopen_s() is never inherited by child processes launched using CreateProcess().

Otherwise, file rotation will fail since the old log file is still opened by the child process and we cannot rename it.

include/spdlog/details/os.h

@@ -153,6 +153,13 @@ inline bool fopen_s(FILE **fp, const filename_t &filename, const filename_t &mod
 #else
     *fp = _fsopen((filename.c_str()), mode.c_str(), _SH_DENYNO);
 #endif
+
+	// Make sure the file handle is never inherited by child processes created using CreateProcess().
+	// Otherwise, file rotation will fail since the file is left open by the child process.
+	auto fn = _fileno(*fp);
+	auto handle = HANDLE(_get_osfhandle(fn));
+	::SetHandleInformation(handle, HANDLE_FLAG_INHERIT, 0);
+
 #else // unix
     *fp = fopen((filename.c_str()), mode.c_str());
 #endif