[PATCH] libstdc++: Fix LD_LIBRARY_PATH when testing an installed compiler

[Arsen Arsenović]

Previously, none would be set, so an installed compiler that does not
emit an RPATH to its libraries would not be able to execute programs
that require libstdc++.so symbols.

libstdc++-v3/ChangeLog:

        * testsuite/lib/libstdc++.exp (libstdc++_init): Use
        gcc-set-multilib-library-path to calculate LD_LIBRARY_PATH for
        installed G++ compilers.
---
Before:

  Setting LD_LIBRARY_PATH to 
:/usr/local/tools/gcc-2025/lib64:/usr/local/tools/gcc-2025/lib
  Execution timeout is: 300
  spawn [open ...]
  ./1.exe: /usr/local/tools/gcc-2025/lib64/libstdc++.so.6: version 
`GLIBCXX_3.4.35' not found (required by ./1.exe)
  FAIL: 23_containers/flat_set/1.cc  -std=gnu++26 execution test

After:

  Setting LD_LIBRARY_PATH to 
:/srv/data/aarsenovic/getting-started/install/lib/gcc/x86_64-none-linux-gnu/17.0.0/../../../../x86_64-none-linux-gnu/lib/../lib64::/srv/data/aarsenovic/getting-started/install/lib/gcc/x86_64-none-linux-gnu/17.0.0/../../../../x86_64-none-linux-gnu/lib/../lib64:/usr/local/tools/gcc-2025/lib64:/usr/local/tools/gcc-2025/lib
  Execution timeout is: 300
  spawn [open ...]
  PASS: 23_containers/flat_set/1.cc  -std=gnu++26 execution test

Other testsuites also seem to do this.

OK?  It may be useful also to backport.

 libstdc++-v3/testsuite/lib/libstdc++.exp | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp 
b/libstdc++-v3/testsuite/lib/libstdc++.exp
index 4ffbf106b6bf..62a04ca10b60 100644
--- a/libstdc++-v3/testsuite/lib/libstdc++.exp
+++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
@@ -75,6 +75,7 @@ load_gcc_lib timeout.exp
 load_gcc_lib timeout-dg.exp
 load_gcc_lib wrapper.exp
 load_gcc_lib target-utils.exp
+load_gcc_lib gcc-defs.exp
 load_gcc_lib dg-test-cleanup.exp
 
 # Useful for debugging.  Pass the name of a variable and the verbosity
@@ -247,13 +248,14 @@ proc libstdc++_init { testfile } {
            }
          }
        }
-
-       set_ld_library_path_env_vars
-       if [info exists env(LD_LIBRARY_PATH)] {
-         verbose -log "LD_LIBRARY_PATH = $env(LD_LIBRARY_PATH)"
-       }
     } else {
        set compiler [transform "g++"]
+       append ld_library_path [gcc-set-multilib-library-path $compiler]
+    }
+
+    set_ld_library_path_env_vars
+    if [info exists env(LD_LIBRARY_PATH)] {
+       verbose -log "LD_LIBRARY_PATH = $env(LD_LIBRARY_PATH)"
     }
 
     # Set the default timeout for v3 tests.
-- 
2.54.0