Ubuntu build break fix, 2nd attempt (#953)

* Fix Ubuntu build break due to cmake upgrade
- New cmake version changes treatment of CMAKE_INSTALL_LIBDIR variable,
  which now evaluates to different things for xerces build and main
  client build.  As a result, we build Xerces, then go looking to link
  to it in the wrong place.  Hard-coding the path to just 'lib' for now
  appears to fix the Ubuntu issue without breaking anything else.

* 2nd attempt to fix Ubuntu build break
- First attempt broke RHEL flavors, and only fixed the first dependent
  library on Ubuntu - gtest was still looked for in the wrong place
- It appears cmake has special code on Ubuntu to use the wrong lib dir
  iff CMAKE_INSTALL_PREFIX is set to /usr or /usr/local, so we'll set it
  to something else and see if that does or doesn't break anything else.

ci/base/base.yml

@@ -99,12 +99,16 @@ builds:
     #@yaml/map-key-override
     params:
       CMAKE_CONFIGURE_FLAGS: "-DCMAKE_INSTALL_PREFIX=/home/build"
+      CMAKE_BUILD_FLAGS: "-j16"
+      CPACK_GENERATORS: "TGZ"
 
   - _: #@ template.replace(new_build("ubuntu-20.04"))
     image_family: build-ubuntu-20-04
     source_image_family: ubuntu-2004-lts
     #@yaml/map-key-override
     params:
       CMAKE_CONFIGURE_FLAGS: "-DCMAKE_INSTALL_PREFIX=/home/build"
+      CMAKE_BUILD_FLAGS: "-j16"
+      CPACK_GENERATORS: "TGZ"
 
 configs: [ ]