Fix build with Poppler 0.86 and later.

Taken from Arch Linux, but adjusted to patch the versioned Poppler
files, as upstream applies it after copying them in place.
https://git.archlinux.org/svntogit/packages.git/tree/trunk/texlive-poppler-0.86.patch?h=packages/texlive-bin

--- a/texk/web2c/pdftexdir/pdftoepdf-poppler0.76.0.cc	2020-03-03 21:11:35.102711802 +0000
+++ b/texk/web2c/pdftexdir/pdftoepdf-poppler0.76.0.cc	2020-03-03 21:13:13.057420111 +0000
@@ -757,7 +757,7 @@
     if (page_name) {
         // get page by name
         GString name(page_name);
-        LinkDest *link = pdf_doc->doc->findDest(&name);
+        LinkDest *link = pdf_doc->doc->findDest(&name).get();
         if (link == 0 || !link->isOk())
             pdftex_fail("PDF inclusion: invalid destination <%s>", page_name);
         Ref ref = link->getPageRef();