Rebase executable to match relocated base address

Windows executables linked with -dynamicbase get a new base address
when loaded, which makes debugging impossible if the executable isn't
also rebased in gdb.

The new base address is read from the Process Environment Block.

gdb/ChangeLog:

2020-03-03  Hannes Domani  <ssbssa@yahoo.de>

	* windows-tdep.c (windows_solib_create_inferior_hook): New function.
	(windows_init_abi): Set and use windows_so_ops.