Bug#996802: llvm-toolchain-12: FTBFS on s390x since 1:12.0.1-10: Cannot find builtins library for the target architecture

[Simon McVittie]

Source: llvm-toolchain-12
Version: 1:12.0.1-10
Severity: serious
Tags: ftbfs
Justification: fails to build from source (but built successfully in the past)

The restructuring in 1:12.0.1-10 seems to have caused a regression on s390x:

https://buildd.debian.org/status/fetch.php?pkg=llvm-toolchain-12&arch=s390x&ver=1%3A12.0.1-10&stamp=1634250418&raw=0
> -- Compiler-RT supported architectures: s390x
> CMake Error at /<<PKGBUILDDIR>>/compiler-rt/cmake/Modules/AddCompilerRT.cmake:243 (message):
>   Cannot find builtins library for the target architecture
> Call Stack (most recent call first):
>   /<<PKGBUILDDIR>>/compiler-rt/lib/stats/CMakeLists.txt:23 (add_compiler_rt_runtime)