Silence ARM inline asm warning in libunwind (dotnet#38971)

The libunwind headers define unw_getcontext in the libunwind headers for ARM
as inline assembly with stmia instruction storing SP and PC, which clang
complains about as deprecated. However, it is required for atomic restoration
of the context, so disable that warning.

This change silences that warning.

src/coreclr/src/pal/src/exception/seh-unwind.cpp

@@ -317,7 +317,18 @@ BOOL PAL_VirtualUnwind(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextP
     }
 
 #if !UNWIND_CONTEXT_IS_UCONTEXT_T
+// The unw_getcontext is defined in the libunwind headers for ARM as inline assembly with
+// stmia instruction storing SP and PC, which clang complains about as deprecated.
+// However, it is required for atomic restoration of the context, so disable that warning.
+#if defined(__llvm__) && defined(TARGET_ARM)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Winline-asm"
+#endif
     st = unw_getcontext(&unwContext);
+#if defined(__llvm__) && defined(TARGET_ARM)
+#pragma clang diagnostic pop
+#endif
+
     if (st < 0)
     {
         return FALSE;