Don't use the remote pool when using clang-tidy

In Make, clang-tidy and clang run in the same action, but only clang can
be remoted via RBE/GOMA. So to prevent running up to 500 clang-tidy
instances at the same time and overloading the machine, use the local
pool when using clang-tidy. This does limit the parallelism of the clang
actions attached to clang-tidy, but hopefully that's not that much of a
problem. Clang-tidy isn't enabled by default (opt-in per-build /
per-module), and Soong does not run into this problem.

Bug: 162615762
Test: m WITH_TIDY=1 nothing; build-aosp_flame.ninja is identical before/after
Test: use_rbe m WITH_TIDY=1; inspect build-aosp_flame.ninja, see local_pool
Change-Id: I7dd196fcf4183d175b9608d3d48cdcdf81b514ce
Merged-In: I7dd196fcf4183d175b9608d3d48cdcdf81b514ce