Align ARM constant pool islands via their basic block.

Previously, all ARM::CONSTPOOL_ENTRY instructions had a hardwired
alignment of 4 bytes emitted by ARMAsmPrinter.  Now the same alignment
is set on the basic block.

This is in preparation of supporting ARM constant pool islands with
different alignments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145890 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMAsmPrinter.cpp

@@ -1481,11 +1481,10 @@ void ARMAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     /// in the function.  The first operand is the ID# for this instruction, the
     /// second is the index into the MachineConstantPool that this is, the third
     /// is the size in bytes of this constant pool entry.
+    /// The required alignment is specified on the basic block holding this MI.
     unsigned LabelId = (unsigned)MI->getOperand(0).getImm();
     unsigned CPIdx   = (unsigned)MI->getOperand(1).getIndex();
 
-    EmitAlignment(2);
-
     // Mark the constant pool entry as data if we're not already in a data
     // region.
     OutStreamer.EmitDataRegion();