Commit 4656e3d66 replaced the "#define CLOBBER_CACHE_ALWAYS"
testing mechanism with a GUC, which has been a great help for
doing cache-clobber testing in more efficient ways; but there
is a gap in the implementation. The only way to do cache-clobber
testing during an initdb run is to use the old method with #define,
because one can't set the GUC from outside. Improve this by
adding a switch to initdb for the purpose.
(Perhaps someday we should let initdb pass through arbitrary
"-c NAME=VALUE" switches. Quoting difficulties dissuaded me
from attempting that right now, though.)
Back-patch to v14 where 4656e3d66 came in.
Discussion: https://postgr.es/m/1582507.1624227029@sss.pgh.pa.us
b741f4c3ee