bug#58291: 29.0.50; MacOS compilation warning for possibly unitialized use in emacs.c

[Gerd Möllmann]

In GNU Emacs 29.0.50 (build 5, aarch64-apple-darwin21.6.0, NS
 appkit-2113.60 Version 12.6 (Build 21G115)) of 2022-10-04 built on
 Mini.fritz.box
Repository revision: 849b7756fd31a69791e67dfe010b1e10f0168c83
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2113
System Description:  macOS 12.6

This is latest master as of writing this.  When compiling emacs, I see

emacs.c:899:7: warning: variable 'bufsize' is used uninitialized whenever 'if' 
condition is true [-Wsometimes-uninitialized]
  if (!(emacs_executable && *emacs_executable))
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
emacs.c:964:7: note: uninitialized use occurs here
  if (bufsize < needed)
      ^~~~~~~
emacs.c:899:3: note: remove the 'if' if its condition is always false
  if (!(emacs_executable && *emacs_executable))
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
emacs.c:928:3: note: variable 'bufsize' is declared here
  ptrdiff_t bufsize = exenamelen + strlen (suffix) + 1;
  ^
emacs.c:1755:17: warning: 'fork' is deprecated: Use posix_spawn or fork 
[-Wdeprecated-declarations]
            f = fork ();  /* in orig */