Bug#878236: lwt: FTBFS on armel, mips* and some non-release architectures: Cannot find (any matches for) "/usr/lib/ocaml/lwt/dlllwt-unix_stubs.so" (tried in ., debian/tmp)

[Simon McVittie <smcv@debian.org>]

Source: lwt
Version: 2.7.1-1
Severity: serious
Justification: fails to build from source (but built successfully in the past)
Control: block 871469 by -1

https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=armel&ver=2.7.1-1&stamp=1507629485&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=mips&ver=2.7.1-1&stamp=1507629275&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=mips64el&ver=2.7.1-1&stamp=1507634735&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=mipsel&ver=2.7.1-1&stamp=1507630307&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=alpha&ver=2.7.1-1&stamp=1507630228&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=hppa&ver=2.7.1-1&stamp=1507630640&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=m68k&ver=2.7.1-1&stamp=1507632601&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=sh4&ver=2.7.1-1&stamp=1507630304&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=sparc64&ver=2.7.1-1&stamp=1507629735&raw=0
https://buildd.debian.org/status/fetch.php?pkg=lwt&arch=x32&ver=2.7.1-1&stamp=1507629729&raw=0

dh_install: Cannot find (any matches for) "/usr/lib/ocaml/lwt/dlllwt-unix_stubs.so" (tried in ., debian/tmp)
dh_install: liblwt-ocaml missing files: /usr/lib/ocaml/lwt/dlllwt-unix_stubs.so
dh_install: Cannot find (any matches for) "/usr/lib/ocaml/lwt/dlllwt-glib_stubs.so" (tried in ., debian/tmp)
dh_install: liblwt-glib-ocaml missing files: /usr/lib/ocaml/lwt/dlllwt-glib_stubs.so
dh_install: missing files, aborting

These logs also mention

findlib: [WARNING] Interface topdirs.cmi occurs in several directories: /usr/lib/ocaml/compiler-libs, /usr/lib/ocaml

but unlike the other bug that I just opened, this doesn't seem to cause
any ill effects and the build continues, to fail later.

I don't know what's different about these platforms when compared with
the ones with the other class of FTFBS - perhaps just version skew?
There's no obvious correlation with endianness or word size.

Regards,
    smcv