Don't duplicate -rpath for TBB

[WardBrian]

Summary

Reported on the forums, some versions of ld are now issuing warnings for repeated copies of -rpath.
I think the fact that we were passing it twice already was an error/misinterpretation of LDFLAGS and LDLIBS.

Tests

Side Effects

Release notes

Fixed the RPATH to the TBB library being passed twice on the command line

Checklist

• Math issue #(issue number)

• Copyright holder: (fill in copyright holder information)

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[WardBrian]

@andrjohns is the failure here related to #2947 ?

[andrjohns]

@andrjohns is the failure here related to #2947 ?

Looks like it was just a temporary download error, restart the actions run and all seems to be fine

[andrjohns]

LGTM!