ci/build_libs.sh: update configure options

Remove --build and --host since they are only needed for crosscompile.
Native builds don't need those and they will not work in case someone
tries build on 32bit.

Also add envronment variables for libdir and libexecdir so the
debian/ubuntu specific lib(exec)dir can be overridden.

ci/build_libs.sh

@@ -2,9 +2,19 @@
 
 XFCE_BASE=https://gitlab.xfce.org
 
-AUTOGEN_OPTIONS="--disable-debug --enable-maintainer-mode --host=x86_64-linux-gnu
-                --build=x86_64-linux-gnu --prefix=/usr --libdir=/usr/lib/x86_64-linux-gnu
-                --libexecdir=/usr/lib/x86_64-linux-gnu --sysconfdir=/etc --localstatedir=/var --enable-gtk-doc"
+: ${libdir:="/usr/lib/x86_64-linux-gnu"}
+: ${libexecdir:="/usr/lib/x86_64-linux-gnu"}
+
+AUTOGEN_OPTIONS="
+  --disable-debug
+  --enable-maintainer-mode
+  --prefix=/usr
+  --libdir=$libdir
+  --libexecdir=$libexecdir
+  --sysconfdir=/etc
+  --localstatedir=/var
+  --enable-gtk-doc
+"
 
 # list of git repos in build order
 REPOS="${XFCE_BASE}/xfce/xfce4-dev-tools.git