Bug#916829: libapr1-dev is broken on unmerged /usr

[Helmut Grohne <helmut@subdivi.de>]

Package: libapr1-dev
Architecture: arm64
Version: 1.6.5-1
Severity: serious
User: helmutg@debian.org
Usertags: rebootstrap
Control: affects -1 + src:apr-util

$ grep /usr/bin/sed /usr/share/apr-1.0/build/libtool
SED="/usr/bin/sed"
$

That doesn't work on unmerged /usr. It breaks building apr-util:

https://tests.reproducible-builds.org/debian/rbuild/unstable/arm64/apr-util_1.6.1-3.rbuild.log.gz
| /usr/share/apr-1.0/build/libtool: line 911: /usr/bin/sed: No such file or directory

Also please fix #489625. Doing so automatically fixes this bug.

Helmut