Bug#897275: llvm-6.0 should provide a pkg-config file

[Helmut Grohne]

Package: llvm-6.0
Filename: /usr/lib/llvm-6.0/bin/llvm-config
Forwarded: https://bugs.llvm.org/show_bug.cgi?id=9405
Tags: upstream
User: helmutg at debian.org
Usertags: rebootstrap
Control: affects -1 + src:qtcreator

llvm-6.0 ships a llvm-config tool for discovering aspects such as
libdir. I have no clue what prevented upstream from using the
well-established pkg-config mechanism, but the present llvm-config is
completely unusable for cross compilation:
 * You cannot query the build llvm-config, because it gives you the
   wrong values.
 * You cannot query the host llvm-config, because Exec format error.

Others have recognized that llvm-config is a repetition of a widley
known mistake:
 * https://bugs.llvm.org/show_bug.cgi?id=9405
 * https://bugs.chromium.org/p/chromium/issues/detail?id=219369

Others are implementing workarounds now:
 * https://github.com/voidlinux/void-packages/issues/1531
 * https://github.com/mesonbuild/meson/issues/3327

There even is a tool to derive the .pc file from llvm-config:
 * https://hackage.haskell.org/package/llvm-pkg-config

Helmut