bazel/toolchains/mongo_toolchain_flags.bzl currently defines a number of search paths for the compilers in the toolchain to use for header includes and libraries among other compilation inputs. These paths are hardcoded for the Clang and GCC version numbers used by the toolchain. Build support for these paths to be inferred dynamically from the toolchain itself, or at least to be configurable so that their values can reflect the toolchain chosen (i.e. by the variables file passed to SCons or as configured in the bazel build command line invocation).