appveyor.yml: pass --needed option to pacman

so it won't attempt reinstalling packages which are already installed

appveyor.yml

@@ -45,7 +45,7 @@ build_script:
   - 'if "%compiler%"=="msvc" msbuild harfbuzz.sln /p:Configuration=%configuration% /p:Platform=%platform%'
   - 'if "%compiler%"=="msvc" if not "%platform%"=="ARM" ctest --output-on-failure -C %configuration%'
 
-  - 'if "%compiler%"=="msys2" C:\msys64\usr\bin\bash -lc "pacman --noconfirm -S mingw-w64-$MSYS2_ARCH-{freetype,cairo,icu,gettext,gobject-introspection,gcc,gcc-libs,glib2,graphite2,pkg-config,python2}"'
+  - 'if "%compiler%"=="msys2" C:\msys64\usr\bin\bash -lc "pacman --noconfirm -S --needed mingw-w64-$MSYS2_ARCH-{freetype,cairo,icu,gettext,gobject-introspection,gcc,gcc-libs,glib2,graphite2,pkg-config,python2}"'
   - 'if "%compiler%"=="msys2" C:\msys64\usr\bin\bash -lc "curl https://raw.githubusercontent.com/mirror/mingw-w64/023eb04c396d4e8d8fcf604cfababc53dae13398/mingw-w64-headers/include/dwrite_1.h > %MINGW_PREFIX%/%MINGW_CHOST%/include/dwrite_1.h"'
   - 'if "%compiler%"=="msys2" C:\msys64\usr\bin\bash -lc "cd $APPVEYOR_BUILD_FOLDER; PATH=$PATH:/mingw64/bin:/mingw32/bin; ./autogen.sh --with-uniscribe --with-freetype --with-glib --with-gobject --with-cairo --with-icu --with-graphite2 --with-directwrite --build=%MINGW_CHOST% --host=%MINGW_CHOST% --prefix=%MINGW_PREFIX%; make; make check || .ci/fail.sh"'