Disable Qt5 because it is not exported on install

Elemental exports targets which link to Qt5 CMake targets but those are
not loaded when including Elemental via CMake, breaking user libraries.
Ref.: elemental/Elemental#275

files/Debian-Buster/usr/local/bin/make_install_elemental.sh

@@ -66,6 +66,9 @@ fi
 # disable quadmath.h (EL_DISABLE_QUAD) because it requires a non-standard compiler extension (-std=gnu++11).
 #  Ref.: https://github.com/elemental/Elemental/blob/master/include/El/core/limits.hpp#L143
 
+# disable Qt5 because it is not exported and thus builds using Elemental are currently broken,
+#  Ref.: https://github.com/elemental/Elemental/pull/275
+
 # set minimal possible language level and disable compiler extensions to ease inclusion in own projects
 cat << 'EOF' | patch -p0 --forward --reject-file=- || true
 --- CMakeLists.txt.orig 2018-07-27 07:52:10.460430024 +0000
@@ -115,7 +118,7 @@ cd build/
 sudo -u "$USERNAME" cmake \
     -DCMAKE_BUILD_TYPE=Debug \
     -DBINARY_SUBDIRECTORIES=OFF \
-    -DEL_USE_QT5=ON \
+    -DEL_USE_QT5=OFF \
     -DEL_TESTS=ON \
     -DEL_EXAMPLES=ON \
     -DEL_HYBRID=ON \