appveyor: fix openblas symbol .def filename + missing msvc export library

The name of the generated export file seems to have been changed from
libopenblas.def to $(LIBPREFIX).def in OpenBLAS, probably in their
commit dddedbab

Author: pv

appveyor/build_openblas.sh

@@ -90,11 +90,7 @@ cd $BUILD_BITS/lib
 # At least for the mingwpy wheel, we have to use the VC tools to build the
 # export library. Maybe fixed in later binutils by patch referred to in
 # https://sourceware.org/ml/binutils/2016-02/msg00002.html
-if [ "$INTERFACE64" == "1" ]; then
-    cp ${our_wd}/OpenBLAS/exports/${DLL_BASENAME}.def ${DLL_BASENAME}.def
-else
-    cp ${our_wd}/OpenBLAS/exports/libopenblas.def ${DLL_BASENAME}.def
-fi
+cp ${our_wd}/OpenBLAS/exports/${DLL_BASENAME}.def ${DLL_BASENAME}.def
 "$VC9_ROOT/bin/lib.exe" /machine:${vc_arch} /def:${DLL_BASENAME}.def
 cd ../..
 # Build template site.cfg for using this build