Fix PR ld/24574

This restores a line that has been dropped when the auto-import feature
of the PE-COFF linker was overhauled about one year.  It is necessary
for GDB to properly resolve extern symbol in DLLs.

ld/ChangeLog
	* pe-dll.c (pe_find_data_imports): Replace again the original name
	of the undefined symbol with the __imp_ prefixed one after it is
	resolved.