[runtimes] Use add_lit_testsuite to register lit testsuites

The runtimes build uses variables set by add_lit_testsuite to collect
testsuites from all the runtimes.

Differential Revision: https://reviews.llvm.org/D97913

GitOrigin-RevId: e1173c8794f4942d2cdddb090489ba5a6cc193e8
1 file changed