Fix RPATHs for cc toolchain solib when sibling layout is used (#17506)

This should fix issue #16956

Includes the following changes:

- Refactor logics to find runtime library search directories
- Correctly compute RPATHs for toolchain solib.

Closes #17276.

PiperOrigin-RevId: 509815187
Change-Id: I7f2a2412aea6430fa712dd2836e18f9536757753
(cherry picked from commit 773d232)

Co-authored-by: kshyanashree <109167932+kshyanashree@users.noreply.github.com>