Toolchain not detected in rules_foreign_cc

When using the local toolchain, everything builds fine. When using the hermetic tool chain from this repo, some build systems fail to use the compiler for a simple test program.

Reproduction example in https://github.com/bazel-contrib/rules_foreign_cc/pull/1295.

Start with the reproduction example in rules_foreign_cc pull request #1295 and compare the local and hermetic toolchain behavior for the simple test program. Trace how the compiler is selected and confirm the failing build systems can use the hermetic compiler successfully.

Written by the indexing model from the issue text.