HPCC-9124 Avoid issues with out of date precompiled headers

Anyone installing 4.0 then downgrading to 3.x may get weird behaviour caused
by out-of-date precompiled headers.

Renaming the base header file should help mitigate this issue.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4222 from richardkchapman/eclinclude-rename

HPCC-9124 Avoid issues with out of date precompiled headers

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>