Let -fsanitize-memory-param-retval be used together with
-fsanitize=kernel-memory, so that it can be applied when building the
Linux kernel.
Also add clang/test/CodeGen/kmsan-param-retval.c to ensure that
-fsanitize-memory-param-retval eliminates shadow accesses for parameters
marked as undef.
Reviewed By: eugenis, vitalybuka
Differential Revision: https://reviews.llvm.org/D127860
Alexander Potapenko