libiberty: Fix pex_unix_wait return type

libiberty: Fix pex_unix_wait return type

The recent warning patches broke Solaris bootstrap:

/vol/gcc/src/hg/master/local/libiberty/pex-unix.c:326:3: error: initialization of 'pid_t (*)(struct pex_obj *, pid_t,  int *, struct pex_time *, int,  const char **, int *)' {aka 'long int (*)(struct pex_obj *, long int,  int *, struct pex_time *, int,  const char **, int *)'} from incompatible pointer type 'int (*)(struct pex_obj *, pid_t,  int *, struct pex_time *, int,  const char **, int *)' {aka 'int (*)(struct pex_obj *, long int,  int *, struct pex_time *, int,  const char **, int *)'} [-Wincompatible-pointer-types]
  326 |   pex_unix_wait,
      |   ^~~~~~~~~~~~~
/vol/gcc/src/hg/master/local/libiberty/pex-unix.c:326:3: note: (near initialization for 'funcs.wait')

While pex_funcs.wait expects a function returning pid_t, pex_unix_wait
currently returns int.  However, on Solaris pid_t is long for 32-bit,
but int for 64-bit.

This patches fixes this by having pex_unix_wait return pid_t as
expected, and like every other variant already does.

Bootstrapped without regressions on i386-pc-solaris2.11,
sparc-sun-solaris2.11, x86_64-pc-linux-gnu, and
x86_64-apple-darwin23.1.0.

2023-12-03  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	libiberty:
	* pex-unix.c (pex_unix_wait): Change return type to pid_t.