For MemorySanitizer builds which do not have Reactor routine
instrumentation enabled, mark all Call() arguments as initialized by
calling __msan_unpoison_param(). This prevents false positives.

Note that we also already unpoisoned all memory writes, when proper
instrumentation is not enabled. While it's preferable to set
REACTOR_ENABLE_MEMORY_SANITIZER_INSTRUMENTATION=1 to avoid the false
negatives caused by unpoisoning, it currently causes slowdowns which
result in timeouts.

Bug: b/187467599
Change-Id: I5fdcbceb5cd795f5e3684df0cdc1ba6c1bef06e9
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/54348
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>