Auto merge of #36242 - semarie:local-rebuild, r=alexcrichton

Use libraries from local-rust-root directory in configure when using …

…--enable-local-rebuild

When using --enable-local-rebuild configure options, the configure
script will test rustc version. But when running it, it will not use the
libraries in the local-rust-root directory.

So use `LD_LIBRARY_PATH` environment variable to correct it.

Under OpenBSD, we use `--enable-local-rebuild` for rebuilding rustc-1.11.0 using rustc-1.11.0. But as it is in use in -current (the developpment branch of OpenBSD), system libraries could easily have ABI/API changes. The (unofficial) bootstrap (rustc-1.11.0 used for building rustc-1.11.0) include several system libraries to permit it to run. The build system use libraries in stage0/lib directory. But the configure script doesn't.

Due to my special use of `--enable-local-rebuild`, I dunno if this PR is suitable for inclusion. But it corrects a difference between build and configure use of the binary.

r? @alexcrichton

diff --cc configure
Simple merge