testsuite: don't use host cpu features when testing cross ghc

This patch disables CPU feature detection logic when testing cross
GHC, since those features don't make sense for the target anyway.

(cherry picked from commit b4c3c340)

testsuite/driver/cpu_features.py

@@ -17,6 +17,9 @@ SUPPORTED_CPU_FEATURES = {
 cpu_feature_cache = None
 
 def get_cpu_features():
+    # Don't use host cpu features when testing cross ghc.
+    if config.cross:
+        return []
     try:
         # This import might fail, e.g. if "ctypes" is not available,
         # in which case we report the empty set of features.