Small tweak to embedding.md (#34422)

Adds -rpath to the link line which was suggested in #28982 and removes the line about JULIA_BINDIR, which isn't necessary anymore, since we autodetect the directory. Also remove the reference to libstdc++. If you built julia yourself, it's definitely compatible with the system one. If not, we now build julia binary distributions with wide compatibility with different libstdc++ versions, so the system one should be fine.

Author: Keno

doc/src/manual/embedding.md

@@ -41,12 +41,9 @@ and link against `libjulia`. For instance, when Julia is installed to `$JULIA_DI
 the above test program `test.c` with `gcc` using:
 
 ```
-gcc -o test -fPIC -I$JULIA_DIR/include/julia -L$JULIA_DIR/lib test.c -ljulia $JULIA_DIR/lib/julia/libstdc++.so.6
+gcc -o test -fPIC -I$JULIA_DIR/include/julia -L$JULIA_DIR/lib -Wl,-rpath,$JULIA_DIR/lib test.c -ljulia
 ```
 
-Then if the environment variable `JULIA_BINDIR` is set to `$JULIA_DIR/bin`, the output `test` program
-can be executed.
-
 Alternatively, look at the `embedding.c` program in the Julia source tree in the `test/embedding/` folder.
 The file `ui/repl.c` program is another simple example of how to set `jl_options` options while
 linking against `libjulia`.