Bug#762702: qtbase-opensource-src: FTBFS on arm64

[Edmund Grimley Evans <edmund.grimley.evans@gmail.com>]

Package: qtbase-opensource-src
Version: 5.3.2+dfsg-2

See:

https://buildd.debian.org/status/package.php?p=qtbase-opensource-src&suite=sid

The error is this:

.obj/qcryptographichash.o: In function `__bswap_32':
/usr/include/aarch64-linux-gnu/bits/byteswap.h:46: undefined reference
to `MD5Context::MD5Context()'
collect2: error: ld returned 1 exit status

It appears to have something to do with precompiled headers as the
link succeeded when I compiled qcryptographichash.o without -include
.pch/Qt5Core.

Also, the package was built successfully when I changed

no_pch_architectures := none

to

no_pch_architectures := arm64

in debian/rules.

As this package is a major blocker for arm64 (see
https://people.debian.org/~wookey/bootstrap/blockerlist), could this
change be made in the next version, perhaps, at least as a temporary
measure until the underlying problem can be solved?