add a testcase for a bug Duncan pointed out.

llvm-svn: 46372

llvm/test/CFrontend/2008-01-25-ByValReadNone.c

+// RUN: %llvmgcc -O3 -S -o - -emit-llvm %s | grep readonly
+// RUN: %llvmgcc -O3 -S -o - -emit-llvm %s | not grep readnone
+
+
+// The struct being passed byval means that we need to mark the 
+// function readonly instead of readnone.  Readnone would allow
+// stores to the arg to be deleted in the caller.
+struct S { int A[1000]; };
+int __attribute__ ((const)) f(struct S x) { return x.A[0]; }
+