[test] Correctly include build llvm_shlib_dir in stand-alone builds

[mgorny]

Summary

Add the build llvm_shlib_dir into LD_LIBRARY_PATH before the directory
specified as llvm_libs_dir, in order to fix stand-alone builds
attempting to use installed clang libraries.

In case of stand-alone builds llvm_libs_dir specifies the location of
installed LLVM libraries which can also contain an older version
(previous build) of clang libraries. Therefore, ensure to specify
llvm_shlib_dir (which is always the build tree path) before
the potentially-system llvm_libs_dir.

[mgorny]

Ping.

[beanz]

test/lit.cfg

109

Should this really be fatal? It seems to me in many cases you might not need this to be set.

[mgorny]

test/lit.cfg

109

I don't mind either way. I left it like this since I really don't see a case when it could be unset ;-).

[beanz]

LGTM!

test/lit.cfg

109

Ah! You're right. I didn't see where it was getting set.

test/lit.cfg

if clang_obj_root is not None:
     if not clang_tools_dir:
         lit_config.fatal('No Clang tools dir set!')
     llvm_tools_dir = getattr(config, 'llvm_tools_dir', None)
     if not llvm_tools_dir:
         lit_config.fatal('No LLVM tools dir set!')
     path = os.path.pathsep.join((
             clang_tools_dir, llvm_tools_dir, config.environment['PATH']))
     config.environment['PATH'] = path
+    # in stand-alone builds, llvm_shlib_dir is clang's build tree
+    # while llvm_libs_dir is installed LLVM (and possibly older clang)
+    llvm_shlib_dir = getattr(config, 'llvm_shlib_dir', None)
+    if not llvm_shlib_dir:
+        lit_config.fatal('No LLVM shlib dir set!')
     llvm_libs_dir = getattr(config, 'llvm_libs_dir', None)
     if not llvm_libs_dir:
         lit_config.fatal('No LLVM libs dir set!')
-    path = os.path.pathsep.join((llvm_libs_dir,
+    path = os.path.pathsep.join((llvm_shlib_dir, llvm_libs_dir,
                                  config.environment.get('LD_LIBRARY_PATH','')))
     config.environment['LD_LIBRARY_PATH'] = path
 
 # Propagate path to symbolizer for ASan/MSan.
 for symbolizer in ['ASAN_SYMBOLIZER_PATH', 'MSAN_SYMBOLIZER_PATH']:
     if symbolizer in os.environ:
         config.environment[symbolizer] = os.environ[symbolizer]