[OpenMP] Add missing -L to libomptarget tests

[jdenny]

Summary

Without this patch, if an incompatible libomptarget.so is present in a
system directory, such as /usr/lib64, check-openmp fails many
libomptarget tests with linking errors. The problem appears to have
started at D129875, which landed as dc52712a0632. This patch extends
the libomptarget test suite config with a -L for the current build
directory of libomptarget.so.

[jhuber6]

Surprised this didn't come up sooner.

[JonChesterfield]

Interesting. I wonder what libraries were being picked up before - maybe from the cmake install directory?

L is simpler than linking the specific libraries individually. There's a failure mode where the libraries aren't in the expected directory and other libraries with the same name are found elsewhere, but hopefully cmake errors observably if the library didn't build.

[jdenny]

In D149391#4303774, @JonChesterfield wrote:

Interesting. I wonder what libraries were being picked up before - maybe from the cmake install directory?

Do you mean before dc52712a0632? My understanding is that libomptarget.so was located in a different build directory then, so the existing -L flags in the lit config were sufficient.

[jdenny]

In D149391#4303774, @JonChesterfield wrote:

Interesting. I wonder what libraries were being picked up before - maybe from the cmake install directory?

Revisiting this today, I think that "before" might mean "before the patch under review". When Clang invokes ld, it first passes -L from its own command line (in this case specified in the lit config), then -L for system directories, and then -L for the build's lib directory. That should make it clear why it normally works fine if there's no libomptarget.so in a system directory, and otherwise the Clang command line needs a -L for the build's lib directory to avoid it.

openmp/libomptarget/test/lit.cfg

 config.test_exec_root = config.libomptarget_obj_root
 
 # test format
 config.test_format = lit.formats.ShTest()
 
 # compiler flags
 config.test_flags = " -I " + config.test_source_root + \
     " -I " + config.omp_header_directory + \
-    " -L " + config.library_dir;
+    " -L " + config.library_dir + \
+    " -L " + config.llvm_lib_directory
 
 if config.omp_host_rtl_directory:
     config.test_flags = config.test_flags + " -L " + \
         config.omp_host_rtl_directory
 
 config.test_flags = config.test_flags + " " + config.test_extra_flags
 
 # Allow REQUIRES / UNSUPPORTED / XFAIL to work