Silence GCC 7 warning

GCC 7 was reporting "enumeral and non-enumeral type in conditional expression"
as a warning.
The code casts an instruction opcode enum to unsigned implicitly, in
line with intentions; so this commit silences the warning by making the
cast to unsigned explicit.

llvm/lib/Target/AArch64/AArch64FastISel.cpp

@@ -3270,7 +3270,8 @@ bool AArch64FastISel::fastLowerCall(CallLoweringInfo &CLI) {
   // Issue the call.
   MachineInstrBuilder MIB;
   if (Subtarget->useSmallAddressing()) {
-    const MCInstrDesc &II = TII.get(Addr.getReg() ? getBLRCallOpcode(*MF) : AArch64::BL);
+    const MCInstrDesc &II =
+        TII.get(Addr.getReg() ? getBLRCallOpcode(*MF) : (unsigned)AArch64::BL);
     MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, II);
     if (Symbol)
       MIB.addSym(Symbol, 0);

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp

@@ -776,7 +776,7 @@ bool AArch64CallLowering::isEligibleForTailCallOptimization(
 static unsigned getCallOpcode(const MachineFunction &CallerF, bool IsIndirect,
                               bool IsTailCall) {
   if (!IsTailCall)
-    return IsIndirect ? getBLRCallOpcode(CallerF) : AArch64::BL;
+    return IsIndirect ? getBLRCallOpcode(CallerF) : (unsigned)AArch64::BL;
 
   if (!IsIndirect)
     return AArch64::TCRETURNdi;