Add unit test

Author: zyedidia

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -7201,6 +7201,7 @@ bool AArch64AsmParser::parseDirectiveArch(SMLoc L) {
   }
   FeatureBitset Features = ComputeAvailableFeatures(STI.getFeatureBits());
   setAvailableFeatures(Features);
+
   getTargetStreamer().emitDirectiveArch(Name);
   return false;
 }

llvm/test/MC/AArch64/arch_directive.s

@@ -0,0 +1,13 @@
+# RUN: llvm-mc -assemble -triple=aarch64- %s | FileCheck %s
+# CHECK: .text
+# CHECK-NEXT: .arch armv8-a+lse
+# CHECK-NEXT: cas x0, x1, [x2]
+# CHECK-NEXT: .arch armv8-a
+# CHECK-NEXT: .arch_extension lse
+# CHECK-NEXT: cas x0, x1, [x2]
+.text
+.arch armv8-a+lse
+cas x0, x1, [x2]
+.arch armv8-a
+.arch_extension lse
+cas x0, x1, [x2]