[libc++][NFC] Rename test file according to the libc++ convention

llvm-svn: 357588

diff --git a/libcxx/test/std/type_traits/is_nothrow_convertible.pass.cpp b/libcxx/test/std/utilities/meta/meta.rel/is_nothrow_convertible.pass.cpp
similarity index 100%
rename from libcxx/test/std/type_traits/is_nothrow_convertible.pass.cpp
rename to libcxx/test/std/utilities/meta/meta.rel/is_nothrow_convertible.pass.cpp