testsuite: don't attempt to detect host cpu features when testing cross ghc

The testsuite driver CPU feature detection logic only detects host CPU
and only makes sense when we are not testing a cross GHC.

(cherry picked from commit c4c6d714)
(cherry picked from commit 07641012)
(cherry picked from commit 68bc5d72)

testsuite/driver/cpu_features.py

@@ -16,6 +16,11 @@ SUPPORTED_CPU_FEATURES = {
 cpu_feature_cache = None
 
 def get_cpu_features():
+    # we're testing a cross ghc, don't attempt to detect host cpu
+    # configuration
+    if config.target_wrapper is not None:
+        return {}
+
     if config.os in ['mingw32', 'linux'] and os.path.exists('/proc/cpuinfo'):
         f = open('/proc/cpuinfo').read()
         flags = re.search(r'flags\s*:\s*.*$', f, re.M)