Fix overwriting symlinks to directories

This avoids extra misplaced symlinks if rerunning the build scripts.

build-compiler-rt.sh

@@ -22,7 +22,7 @@ fi
 # Add a symlink for i386 -> i686; we normally name the toolchain
 # i686-w64-mingw32, but due to the compiler-rt cmake peculiarities, we
 # need to refer to it as i386 at this stage.
-ln -sf i686-w64-mingw32 $PREFIX/i386-w64-mingw32 || true
+ln -sfn i686-w64-mingw32 $PREFIX/i386-w64-mingw32 || true
 
 cd compiler-rt
 

build-mingw-w64.sh

@@ -33,7 +33,7 @@ make install
 cd ../..
 for arch in $ARCHS; do
     mkdir -p $PREFIX/$arch-w64-mingw32
-    ln -sf ../generic-w64-mingw32/include $PREFIX/$arch-w64-mingw32/include
+    ln -sfn ../generic-w64-mingw32/include $PREFIX/$arch-w64-mingw32/include
 done
 
 cd mingw-w64-crt