pdumper memory allocation (new FIXME)

[Paul Eggert]

While making minor simplifications to src/pdumper.c I noticed that 
pdumper_load has a comment saying it should not call xmalloc, and yet it 
calls xstrdup which works by calling xmalloc. I added a FIXME to point 
out the inconsistency.

The call to xstrdup was added in 2019-01-26T10:08:address@hidden 
(a7974933dd818194de3c9387b95dbd122bcf506c), whose commit message says 
"Use xstrdup instead of strdup, as on MS-Windows the latter uses the 
wrong heap." I thought that with pdumper we no longer have a hybrid 
malloc with two heaps; we simply have the usual C heap. Is that not true 
in MS-Windows for some reason? I'm asking because if there are still 
multiple heaps with pdumper (either on MS-Windows or elsewhere), I 
suspect there will be similar problems elsewhere in the code.