* ldemul.h (ld_emulation_xfer_struct): new hook "recognized_file"

* ldemul.h (ld_emulation_xfer_struct): new hook "recognized_file"
* ldemul.c (ldemul_recognized_file): new function, new hook
* ldint.texinfo: document new hook.
* ldlang.c (load_symbols): call recognized_hook for all objects we
do recognize, in case the emulation needs to handle them
specially.  PE DLLs use this.
* pe-dll.c (pe_dll_generate_def_file): take out hack and debug
printfs
* emultempl/pe.em (gld_i386_recognized_file): new function
(gld_i486_unrecognized_file): take out hack