[Driver] Pass --unwindlib=platform to tests that check unwinder

This addresses an issue which was revealed by D98022.

Differential Revision: https://reviews.llvm.org/D98131

Author: petrhosek

clang/test/Driver/compiler-rt-unwind.c

@@ -2,7 +2,7 @@
 // --unwindlib=XXX properly.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
-// RUN:     --target=x86_64-unknown-linux -rtlib=libgcc \
+// RUN:     --target=x86_64-unknown-linux -rtlib=libgcc --unwindlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:   | FileCheck --check-prefix=RTLIB-GCC %s
 // RTLIB-GCC: "{{.*}}lgcc"