Fix compile errors when building with gcc-12 or clang (partial #12035)

This is a partial cherry-pick from Redis 7.2

## Fix various compilation warnings and errors

5) server.c

COMPILER: gcc-13 with FORTIFY_SOURCE

WARNING:
```
In function 'lookupCommandLogic',
    inlined from 'lookupCommandBySdsLogic' at server.c:3139:32:
server.c:3102:66: error: '*(robj **)argv' may be used uninitialized [-Werror=maybe-uninitialized]
 3102 |     struct redisCommand *base_cmd = dictFetchValue(commands, argv[0]->ptr);
      |                                                              ~~~~^~~
```

REASON: The compiler thinks that the `argc` returned by `sdssplitlen()` could be 0,
resulting in an empty array of size 0 being passed to lookupCommandLogic.
this should be a false positive, `argc` can't be 0 when strings are not NULL.

SOLUTION: add an assert to let the compiler know that `argc` is positive.

## Other changes
1) Fixed `ps -p [pid]`  doesn't output `<defunct>` when using procps 4.x causing `replication
  child dies when parent is killed - diskless` test to fail.

(cherry picked from commit 42c8c61813)

src/server.c

@@ -3060,6 +3060,7 @@ struct redisCommand *lookupCommandBySdsLogic(dict *commands, sds s) {
         return NULL;
     }
 
+    serverAssert(argc > 0); /* Avoid warning `-Wmaybe-uninitialized` in lookupCommandLogic() */
     robj objects[argc];
     robj *argv[argc];
     for (j = 0; j < argc; j++) {

tests/support/util.tcl

@@ -634,7 +634,7 @@ proc get_child_pid {idx} {
 }
 
 proc process_is_alive pid {
-    if {[catch {exec ps -p $pid} err]} {
+    if {[catch {exec ps -p $pid -f} err]} {
         return 0
     } else {
         if {[string match "*<defunct>*" $err]} { return 0 }