Fix linking with clang++ on linux if install_rpath.

mesonbuild/compilers/compilers.py

@@ -860,6 +860,11 @@ class Compiler:
             # Not needed on Windows or other platforms that don't use RPATH
             # https://github.com/mesonbuild/meson/issues/1897
             lpaths = ':'.join([os.path.join(build_dir, p) for p in rpath_paths])
+
+            # clang expands '-Wl,rpath-link,' to ['-rpath-link'] instead of ['-rpath-link','']
+            # This eats the next argument, which happens to be 'ldstdc++', causing link failures.
+            # We can dodge this problem by not adding any rpath_paths if the argument is empty.
+            if lpaths.strip() != '':
                 args += ['-Wl,-rpath-link,'+lpaths]
         return args