Remove svn:executable property

git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@1470 4407c894-4637-0410-b4f5-ada5f102cad1
diff --git a/mingw-w64-doc/howto-build/mingw-w64-howto-build-adv.txt b/mingw-w64-doc/howto-build/mingw-w64-howto-build-adv.txt
old mode 100755
new mode 100644