It looks like you have to compile using the following sequence of commands:
$ make
$ make install

When trying directly with 'make install' my compile failed with the above mentioned 'harfbuzz' errors. Probably your 'make finish' did the same.

You also have to make sure you have correctly configured pkg-config. The error I was seeing previously was due to qt not finding dbus headers because I didn't correctly configure pkg-config.
To correctly configure pkg-config I did the following before running ./configure:
SYSROOT=/mnt/rpi-rootfs
export PKG_CONFIG_DIR=
export PKG_CONFIG_SYSROOT_DIR=$SYSROOT
export PKG_CONFIG_LIBDIR=$SYSROOT/usr/lib/arm-linux-gnueabihf/pkgconfig/:$SYSROOT/usr/share/pkgconfig:$SYSROOT/usr/lib/pkgconfig
export PKG_CONFIG_PATH=$SYSROOT/usr/lib/arm-linux-gnueabihf/pkgconfig/:$SYSROOT/usr/share/pkgconfig:$SYSROOT/usr/lib/pkgconfig

With these settings I was able to successfully build and install Qt 5.4. Hope this helps.