Bug#819072: llvm-3.8-dev: LLVM CMake files broken by Debian packaging

[Brad King]

Package: llvm-3.8-dev
Version: 1:3.8-2
Severity: normal

Dear Maintainer,

Issues similar to those in bug #785931 have returned in the 3.8 package.

When a CMake-based project does

    find_package(LLVM)

on Debian one gets

    CMake Error at /usr/share/llvm-3.8/cmake/LLVMConfig.cmake:178 (include):
      include could not find load file:

        /usr/share/llvm/cmake/LLVMExports.cmake

The reason is explained in this thread on the llvm mailing list:

    http://thread.gmane.org/gmane.comp.compilers.llvm.cvs/255502/focus=255724

Basically upstream LLVM made changes during 3.8 development to make their
CMake packaging files relocatable by computing locations relative to one
another.  However, Debian's packaging changes these relative locations by
moving things around after installation.  Therefore the wrong locations
are computed.

Debian packaging must be taught to patch LLVMConfig.cmake to specify
absolute locations of LLVM_INSTALL_PREFIX, LLVM_CMAKE_DIR, etc. based
on where Debian puts them.

Note that the 'castxml' package requires LLVM/Clang CMake packaging files
to build.  Therefore building that package against a llvm-*-dev package
(and libclang-*-dev) will reveal such problems.

-Brad