[newlib-cygwin] Cygwin: Document recent fixes to release note

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=0d34ce2d787f0eff2e4bb4d483d4344f3f6bc37b

commit 0d34ce2d787f0eff2e4bb4d483d4344f3f6bc37b
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Thu Dec 4 19:50:02 2025 +0900

    Cygwin: Document recent fixes to release note
    
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
    (cherry picked from commit 7d43942e7c3b56799e9e46c4701f86a8eb0ed579)

Diff:
---
 winsup/cygwin/release/3.6.6 | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/winsup/cygwin/release/3.6.6 b/winsup/cygwin/release/3.6.6
new file mode 100644
index 000000000..09b6a3913
--- /dev/null
+++ b/winsup/cygwin/release/3.6.6
@@ -0,0 +1,16 @@
+Fixes:
+------
+
+- Fix the problem that the destructor of dlopen()'ed DLL may be called
+  after dlclose(). This fixes the crash on exiting SDL2.
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-October/258877.html
+
+- Fix the problem that the constructor of dlopen()'ed DLL may be called
+  twice.
+
+- Fix deadlock regarding atexit()'ed function, that waits for another
+  thread which calls atexit().
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-October/258930.html
+
+- Fix the problem that tmp_pathbuf area is destroyed regarding flock().
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-October/258914.html