set HAXEPATH on appveyor as haxelib currently requires it (see HaxeFoundation/haxelib#100)

appveyor.yml

@@ -53,6 +53,7 @@ build_script:
     - '%CYG_ROOT%/bin/bash -lc "cd \"$OLDPWD\" && make -s -f Makefile.win package_src || echo package_src failed"'
     - '%CYG_ROOT%/bin/bash -lc "cd \"$OLDPWD\" && make -s -f Makefile.win"'
     - 'set PATH=%PATH%;%APPVEYOR_BUILD_FOLDER%'
+    - 'set HAXEPATH=%APPVEYOR_BUILD_FOLDER%'
     - '%CYG_ROOT%/bin/bash -lc "cd \"$OLDPWD\" && make -s -f Makefile.win tools"'
     - '%CYG_ROOT%/bin/bash -lc "cd \"$OLDPWD\" && make -s -f Makefile.win package_bin"'
     - dir %APPVEYOR_BUILD_FOLDER%\out