Prefer /lib64 and /usr/lib64 ahead of /lib in the DynamicLibrary test so it
loads the real shared object on multilib lib64 systems instead of failing.

Imported verbatim from ::gentoo (wxGTK-3.2.1-prefer-lib64-in-tests.patch, by
Arsen Arsenović); applies cleanly (fuzz=0) to 3.3.2. Test-only (USE=test).
Upstream ref: https://github.com/wxWidgets/wxWidgets/commit/512b8033feef6ba99c4dfdf6ada42a56d7425d6d

--- a/tests/misc/dynamiclib.cpp
+++ b/tests/misc/dynamiclib.cpp
@@ -37,9 +37,10 @@ TEST_CASE("DynamicLibrary::Load", "[dynlib]")
 #else // other Unix
     static const char* const candidateDirs[] =
     {
+        "/lib64",
+        "/usr/lib64",
         "/lib/x86_64-linux-gnu",
         "/lib",
-        "/lib64",
         "/usr/lib",
     };