trivial: build-windows: fix some shellcheck warnings

contrib/ci/build_windows.sh

@@ -2,8 +2,8 @@
 set -e
 #prep
 export LC_ALL=C.UTF-8
-export DESTDIR=`pwd`/dist
-root=`pwd`
+root=$(pwd)
+export DESTDIR=${root}/dist
 build=$root/build-win32
 rm -rf $DESTDIR $build
 
@@ -12,8 +12,8 @@ mkdir -p $build $DESTDIR && cd $build
 meson .. \
     --cross-file=../contrib/mingw64.cross \
     --prefix=/ \
-    --libexecdir=$target \
-    --bindir=$target \
+    --libexecdir="" \
+    --bindir="" \
     -Dbuild=standalone \
     -Ddocs=none \
     -Dpolkit=false \
@@ -70,7 +70,7 @@ makensis -NOCD $build/contrib/setup-win32.nsi
 cp /usr/x86_64-w64-mingw32/sys-root/mingw/bin/*.dll .
 
 #remove static archives
-find -type f -name "*.dll.a" | xargs rm -f
+find -type f -print0 -name "*.dll.a" | xargs rm -f
 
 #remove stuff that we really don't need
 rm -fr gcab.exe \