gzFile is already a pointer, so code like
gzFile *handle = gzopen(...)
is wrong.
This used to pass silently because gzFile used to be defined as void*,
and you can assign a void* to a void**. But somewhere between zlib
versions 1.2.3.4 and 1.2.6, the definition of gzFile was changed to
struct gzFile_s *, and with that new definition this usage causes
compiler warnings.
So remove all those extra pointer decorations.
There is a related issue in pg_backup_archiver.h, where
FILE *FH; /* General purpose file handle */
is used throughout pg_dump as sometimes a real FILE* and sometimes a
gzFile handle, which also causes warnings now. This is not yet fixed
here, because it might need more code restructuring.
d923125b77