Restore procfs.c compilation

Restore procfs.c compilation

Since c8fbd44a018a9923f906bfd2be5489caa87b602a (gdb: remove
target_is_pushed free function), procfs.c compilation is broken, which
went unnoticed for lack of functioning buildbots:

/vol/src/gnu/gdb/hg/master/dist/gdb/procfs.c: In member function 'virtual void procfs_target::attach(const char*, int)':
/vol/src/gnu/gdb/hg/master/dist/gdb/procfs.c:1772:8: error: 'inf' was not declared in this scope; did you mean 'info'?
 1772 |   if (!inf->target_is_pushed (this))
      |        ^~~
      |        info
/vol/src/gnu/gdb/hg/master/dist/gdb/procfs.c: In member function 'virtual void procfs_target::create_inferior(const char*, const string&, char**, int)':
/vol/src/gnu/gdb/hg/master/dist/gdb/procfs.c:2865:8: error: 'inf' was not declared in this scope; did you mean 'info'?
 2865 |   if (!inf->target_is_pushed (this))
      |        ^~~
      |        info

Fixed by defining inf.  Tested on amd64-pc-solaris2.11 and
sparcv9-sun-solaris2.11.

2021-03-29  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gdb:
	* procfs.c (procfs_target::attach): Define inf.
	Use it.
	(procfs_target::create_inferior): Likewise.