build: Experimental support to build using precompiled headers

This type of build needs to be explicitly enabled using --with-pch
configure option.

Change-Id: I95ba143c91fbb3f829a807b0f54d31ab343e4c3f
ci: Explicitly setting HOME variable (tests were having key generation problem)

Change-Id: I5221afcc967beeb7baf0a2f68c3fbffff80eaf97