[compiler-rt] Speculative fix for cross_over_uniform_dist.test

This change makes the REQUIRES clause unambiguously use triple-relative
feature names, in case that helps fix the bot failure seen at
https://lab.llvm.org/buildbot/#/builders/37/builds/5998

compiler-rt/test/fuzzer/cross_over_uniform_dist.test

@@ -1,4 +1,4 @@
-REQUIRES: linux, x86_64
+REQUIRES: x86_64-, -linux
 RUN: %cpp_compiler %S/KeepSeedTest.cpp -o %t-CrossOverUniformDistTest
 
 RUN: rm -rf %t-corpus