Don't link pthread on QNX

On QNX, pthread is part of libc [1]. There's no separate pthread library
to link.

[1] https://www.qnx.com/developers/docs/7.1/index.html#com.qnx.doc.neutrino.lib_ref/topic/p/pthread_create.html

googletest/test/BUILD.bazel

@@ -95,6 +95,7 @@ cc_test(
         "googletest/test",
     ],
     linkopts = select({
+        "//:qnx": [],
         "//:windows": [],
         "//conditions:default": ["-pthread"],
     }),