Make LLVMRustHasFeature more robust

The function should accept feature strings that old LLVM might not
support.

Simplify the code using the same approach used by
LLVMRustPrintTargetFeatures.

Dummify the function for non 4.0 LLVM and update the tests accordingly.

src/rustllvm/PassWrapper.cpp

@@ -181,20 +181,14 @@ extern "C" bool LLVMRustHasFeature(LLVMTargetMachineRef TM,
   TargetMachine *Target = unwrap(TM);
   const MCSubtargetInfo *MCInfo = Target->getMCSubtargetInfo();
   const FeatureBitset &Bits = MCInfo->getFeatureBits();
-  const llvm::SubtargetFeatureKV *FeatureEntry;
+#if LLVM_VERSION_GE(4, 0)
+  const ArrayRef<SubtargetFeatureKV> FeatTable = MCInfo->getFeatureTable();
 
-#define SUBTARGET(x)                                                           \
-  if (MCInfo->isCPUStringValid(x##SubTypeKV[0].Key)) {                         \
-    FeatureEntry = x##FeatureKV;                                               \
-  } else
-
-  GEN_SUBTARGETS { return false; }
-#undef SUBTARGET
-
-  while (strcmp(Feature, FeatureEntry->Key) != 0)
-    FeatureEntry++;
-
-  return (Bits & FeatureEntry->Value) == FeatureEntry->Value;
+  for (auto &FeatureEntry : FeatTable)
+    if (!strcmp(FeatureEntry.Key, Feature))
+      return (Bits & FeatureEntry.Value) == FeatureEntry.Value;
+#endif
+  return false;
 }
 
 enum class LLVMRustCodeModel {

src/test/run-make/print-cfg/Makefile

@@ -5,7 +5,7 @@ all: default
 	$(RUSTC) --target x86_64-pc-windows-gnu --print cfg | grep x86_64
 	$(RUSTC) --target i686-pc-windows-msvc --print cfg | grep msvc
 	$(RUSTC) --target i686-apple-darwin --print cfg | grep macos
-	$(RUSTC) --target i686-unknown-linux-gnu --print cfg | grep sse2
+	$(RUSTC) --target i686-unknown-linux-gnu --print cfg | grep gnu
 
 ifdef IS_WINDOWS
 default:

src/test/run-pass/sse2.rs

@@ -7,6 +7,7 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
+// min-llvm-version 4.0
 
 #![feature(cfg_target_feature)]