test: add a ODR violation check for the static standard library

The static version of the standard library was leaking symbols in the
`llvm::` namespace which would result in ODR violations were the
artifact linking against `LLVMSupport` (via another dependency).  In
particular, `llvm::SmallVector` and `llvm::StringSwitch` symbols were
being leaked.  This adds a test case specifically for the static variant
of the library.  The dynamic variant of the library is already tested in
a separate test.

Author: compnerd

test/stdlib/llvm-support-odr-violation-static.test-sh

@@ -0,0 +1,5 @@
+// RUN: %llvm-nm --defined-only -C %platform-module-dir/libswiftCore.a | %FileCheck --allow-empty %s
+// CHECK-NOT: [^:]llvm::
+
+// REQUIRES: OS=linux-gnu
+// REQUIRES: static_stdlib