also use cygwin x64

appveyor.yml

@@ -31,8 +31,8 @@ install:
     - '%CYG_ROOT%/bin/bash -lc "echo initialize"'
     - choco install curl
     # Install ocaml
-    - curl -fsSL -o cygwin-setup.exe --retry 3 https://cygwin.com/setup-x86.exe
-    - 'cygwin-setup.exe -g -q -R "%CYG_ROOT%" -P make -P git -P mingw64-i686-zlib -P rsync -P patch -P diffutils -P curl -P unzip -P m4 -P perl -P mingw64-i686-gcc-core -P mingw64-i686-pcre'
+    - curl -fsSL -o cygwin-setup.exe --retry 3 https://cygwin.com/setup-x86_64.exe
+    - 'cygwin-setup.exe -g -q -R "%CYG_ROOT%" -P make -P git -P mingw64-x86_64-zlib -P rsync -P patch -P diffutils -P curl -P unzip -P m4 -P perl -P mingw64-x86_64-gcc-core -P mingw64-x86_64-pcre'
     - if not exist "opam64.tar.xz" (
         curl -fsSL -o opam64.tar.xz --retry 3 https://github.com/fdopen/opam-repository-mingw/releases/download/0.0.0.1/opam64.tar.xz
       )