pw_presubmit: Use correct host compiler for OS
pw_presubmit: Use correct host compiler for OS

Use 'gcc' for host compiler on Windows and 'clang' on all other
platforms. Also allow running the "wrong" compiler in case we try to
support it in the future.

Change-Id: Idd35f62e3041b6b310771a12fc14ae9728ffe04d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/35160
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed