Try to fix external_symbolizer_path.cpp test to stop breaking on buildbots.

Not sure what the issue is, but it might be because the test copies
llvm-symbolizer to a different directory, and it can't find libc++.
Try to add some REQUIRES that we use in other tests where we copy
llvm tools out of their original directories.

compiler-rt/test/sanitizer_common/TestCases/external_symbolizer_path.cpp

@@ -1,3 +1,10 @@
+// If the binary looks up libraries using an rpath, we can't test this
+// without copying the whole lib dir or polluting the build dir.
+// REQUIRES: static-libs
+
+// The above also applies if the binary is built with libc++.
+// UNSUPPORTED: libcxx-used
+
 // REQUIRES: shell
 // REQUIRES: x86-target-arch
 // RUN: rm -rf %t.bin