cygwin: give cygperl*.dll an explicit base address

Cygwin's fork emulation doesn't handle overlapping addresses
between different DLLs, since it tries to lay out the address space
of the child process to match the parent process, but if there's an
address conflict between DLLs, Windows may load those DLLs at
different addresses.

To avoid having to manually assign addresses to each DLL, since
around 5.10 we've used --enable-auto-image-base to assign load
addresses for cygperl*.dll and dynamic extension DLLs and this
has mostly worked well, but as perl has gotten larger and
cygperl*.dll has grown, we've had two cases where there's overlap
between the address space for cygperl*.dll and some extension
DLL, see Perl#22695 and Perl#22104.

This problem occurs because:

- cygperl*.dll is large, and with -DDEBUGGING or some other option
  that increases binary size, even large, occupying more than one of
  the "slots" that the automatic image base code in ld can assign
  the DLL to.

- unlike the extension DLLs, the name of cygperl*.dll changes with
  every release, so we roll the dice each release on whether there
  will be a conflict between cygperl*.dll and some other DLL.

Previously I've added an entry to perldelta and updated the CI
workflow to workaround the conflict, this change should prevent
that particular conflict.

The addresses I've chosen here are "just" (for large values of
"just") below the base address range used by automatic address
space selection.

For 64-bit this was done by inspection, examing the output of
"rebase -i" on the extension DLLs and looking at the source of ld,
in particular:

  https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/emultempl/pep.em;h=00c4ea9e15a765c29b15b621f53d6bfcb499e5ed;hb=HEAD#l144

Note cygwin builds set move_default_addr_high=1 if you read that code.

For 32-bit I just looked at the source:

  https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/emultempl/pe.em;h=52f59b8b#l173

since I don't have a 32-bit cygwin install any more, since cygwin
no longer ship it and it commonly had the fork address conflicts
discussed above.

I would have liked to make the load address configurable via
-Dcygperl_base or similar, but I didn't see a way to get the
base address to pass from Configure through to Makefile.SH.

Fixes Perl#22695

Makefile.SH

@@ -74,6 +74,14 @@ true)
 		;;
 	cygwin*)
 		shrpldflags="$shrpldflags -Wl,--out-implib=libperl.dll.a"
+		# The cygperl dll can be large and has conflicted with
+		# other DLLs as its name has changed from release to release.
+		# Give it its own space (and a lot of it) to work in.
+		# 32-bit (untested) gets less space since it is 32-bit.
+		case "$myarchname" in
+			"x86_64-cygwin") shrpldflags="$shrpldflags -Wl,--image-base=0x00380000000" ;;
+			*)  shrpldflags="$shrpldflags -Wl,--image-base=0x60500000" ;;
+		esac
 		linklibperl="-L. -lperl"
 		;;
 	sunos*)