meta-clang's llvm-config is not compatible with MULTILIBS

[cosmo0920]

Describe the bug
One of the our target boards(RZ/G2E)'s Yocto default conf/local.conf specifies MULTILIBS = "multilib:lib32" and DEFAULTTUNE_virtclass-multilib-lib32 = "armv7vethf-neon" to be able to run 32bit ARMv7 binaries.
So, built binaries will be installed in /usr/lib64/ instead of /usr/lib.

Because our SDK environment does not assume /usr/lib for library installation directory.
Instead, /usr/lib64 is used for 64bit libraries and shared object. And /usr/lib32 is used for 32bit objects.

ref: https://llvm.org/docs/CMake.html#frequently-used-cmake-variables

To Reproduce
Steps to reproduce the behavior:

1. Specify MULTILIBS = "multilib:lib32" and DEFAULTTUNE_virtclass-multilib-lib32 = "armv7vethf-neon" in local.conf
2. Add meta-clang layer
3. bitbake clang-cross-aarch64
4. add meta-browser and meta-rust layer
5. bitbake firefox
6. See error

Error

|  0:05.42 configure: error: compiler is incompatible with sanitize options
|  0:05.42 DEBUG: <truncated - see config.log for full output>
|  0:05.42 DEBUG: /home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot-native/usr/bin/aarch64-poky-linux/aarch64-poky-linux-ld: cannot find /home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot/usr/lib/clang/8.0.1/lib/linux/libclang_rt.builtins-aarch64.a: No such file or directory
|  0:05.42 DEBUG: clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
|  0:05.42 DEBUG: configure: failed program was:
|  0:05.42 DEBUG: #line 2836 "configure"
|  0:05.42 DEBUG: #include "confdefs.h"
|  0:05.42 DEBUG:
|  0:05.42 DEBUG: int main() {
|  0:05.42 DEBUG: XtMalloc()
|  0:05.42 DEBUG: ; return 0; }
|  0:05.42 DEBUG: configure:4123: /home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot-native/usr/bin/aarch64-poky-linux/aarch64-poky-linux-clang -march=armv8-a -mtune=cortex-a53 --rtlib=compiler-rt --stdlib=libc++ -mlittle-endian -Wno-error=unused-command-line-argument -Qunused-arguments --sysroot=/home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot -std=gnu99 -o conftest  -Os -fsigned-char -fno-strict-aliasing -Qunused-arguments  -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed  conftest.c  1>&5
|  0:05.42 DEBUG: /home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot-native/usr/bin/aarch64-poky-linux/aarch64-poky-linux-ld: cannot find /home/vagrant/rzg2-yoshi/build/tmp/work/aarch64-poky-linux/firefox/68.0esr-r0/recipe-sysroot/usr/lib/clang/8.0.1/lib/linux/libclang_rt.builtins-aarch64.a: No such file or directory
|  0:05.42 DEBUG: clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
|  0:05.42 DEBUG: configure: failed program was:
|  0:05.42 DEBUG: #line 4116 "configure"
|  0:05.42 DEBUG: #include "confdefs.h"
|  0:05.42 DEBUG:
|  0:05.42 DEBUG: int main() {
|  0:05.42 DEBUG:
|  0:05.42 DEBUG: ; return 0; }
|  0:05.42 DEBUG: configure: error: compiler is incompatible with sanitize options
|  0:05.42 ERROR: old-configure failed
|  0:05.46 *** Fix above errors and then restart with\
|  0:05.46                "./mach build"
|  0:05.46 client.mk:111: recipe for target 'configure' failed
|  0:05.46 make: *** [configure] Error 1
| WARNING: exit code 2 from a shell command.

Expected behavior
meta-clang's llvm-config can work with DEFAULTTUNE_virtclass-multilib-lib32 specified environment.

llvm-config points to ${RECIPE_SYSROOT}/usr/lib/clang/8.0.1/lib/linux/ but actual libclang libraries are put in ${RECIPE_SYSROOT}/usr/lib64/clang/8.0.1/lib/linux/

LLVM insists that using LLVM_LIBDIR_SUFFIX to control installation directory suffix such as lib64 or lib32.

We should handle library directory glitch it llvm-config with LLVM_LIBDIR_SUFFIX.

Desktop (please complete the following information):

• OS: Ubuntu
• Version 16.04.6 LTS

Additional context

(Updated) I'd encountered this issue during meta-browser's firefox recipe building.

[kraj]

Can you cook up a patch ?

[cosmo0920]

I'm cooking up patches.... 🔨

[kraj]

@cosmo0920 is master we have addressed this issue by using baselib for LIBCXX_CXX_ABI_LIBRARY_PATH and LLVM_LIBDIR_SUFFIX but this patch computes LLVM_LIBDIR_SUFFIX locally using new function get_libdir_suffix is this needed on master as well ?

[cosmo0920]

this patch computes LLVM_LIBDIR_SUFFIX locally using new function get_libdir_suffix is this needed on master as well ?

Yes. Current master's implementation returns empty string on multiarch environment.

[kraj]

Ok then could you prepare a patch for master as well please ? Usually we do the fix on master before backport to release branches

[kraj]

thanks for patch, I think this issue is now fixed.

[cosmo0920]

Yep, this issue is fixed on master.