Bug#972751: llvm-toolchain-9: FTBFS with DEB_BUILD_OPTIONS=reproducible=+fixfilepath

[Vagrant Cascadian]

Package: llvm-toolchain-9
Severity: normal
Tags: patch
User: reproducible-builds at lists.alioth.debian.org
Usertags: fixfilepath ftbfs
X-Debbugs-Cc: reproducible-bugs at lists.alioth.debian.org

When the reproducible=+fixfilepath feature is enabled (either through
DEB_BUILD_OPTIONS, or using a dpkg that enables this by default),
llvm-toolchain-9 fails to build from source:

  http://qa-logs.debian.net/2020/09/26.fixfilepath/llvm-toolchain-9_9.0.1-14_unstable_fixfilepath.log

The fixfilepath feature sets a -ffile-prefix-map flag, which is only
supported in clang-10 or newer.

While the "fixfilepath" feature is not currently enabled in
dpkg-buildflags by default, it may become the default at some point in
the future, and can by triggered manually by setting
DEB_BUILD_OPTIONS=reproducible=+fixfilepath in the build environment.

More information about this issue is available at:

  https://tests.reproducible-builds.org/debian/issues/unstable/ftbfs_due_to_f-file-prefix-map_issue.html
  https://tests.reproducible-builds.org/debian/issues/unstable/ffile_prefix_map_passed_to_clang_issue.html

The attached patch works around this issue by disabling the fixfilepath
feature in debian/rules using DEB_BUILD_MAINT_OPTIONS=-fixfilepath.

Thanks for maintaining llvm-toolchain-9!

live well,
  vagrant
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