build error in libreoffice-android

Hello everyone!
    I am Rutuja and I want to work on libreoffice online android app in
gsoc 2020. I have built libreoffice core and online on ununtu 18.04 but I
am not able to build libreoffice-android. I am getting this error when I
run make command
 'configure: error:
*** expat is required. or try to use --enable-libxml2
/home/rutuja/libreoffice/external/fontconfig/ExternalProject_fontconfig.mk:22:
recipe for target
'/home/rutuja/libreoffice/workdir/ExternalProject/fontconfig/build' failed
make[1]: ***
[/home/rutuja/libreoffice/workdir/ExternalProject/fontconfig/build] Error 1
make[1]: *** Waiting for unfinished jobs....
Makefile:282: recipe for target 'build' failed
make: *** [build] Error'
 I have installed libexpat as well as libexpat-dev package using 'sudo
apt-get install libxml2 libxml2-dev' when i try to install expat it shows

'[sudo] password for rutuja:
Reading package lists... Done
Building dependency tree
Reading state information... Done
expat is already the newest version (2.2.5-3ubuntu0.2).
The following packages were automatically installed and are no longer
required:
  linux-headers-4.15.0-72 linux-headers-4.15.0-72-generic
linux-image-4.15.0-72-generic linux-modules-4.15.0-72-generic
linux-modules-extra-4.15.0-72-generic
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 330 not upgraded.
'

I tried running ./configure --prefix=/usr but I get this error

/home/rutuja/libreoffice/external/liblangtag/ExternalPackage_liblangtag.mk:17:
*** file
/home/rutuja/libreoffice/workdir/UnpackedTarball/liblangtag/liblangtag/.libs/liblangtag-lo.so.1.4.1
does not exist in the tarball.  Stop.
Makefile:282: recipe for target 'build' failed
make: *** [build] Error 2now

How shall I proceed now??
I am following
https://wiki.documentfoundation.org/Development/BuildingForAndroid this
page.

Thank you