[MC] Use .p2align instead of .align

For historic reasons, the behavior of .align differs between targets.
Fortunately, there are alternatives, .p2align and .balign, which make the
interpretation of the parameter explicit, and which behave consistently across
targets.

This patch teaches MC to use .p2align instead of .align, so that people reading
code for multiple architectures don't have to remember which way each platform
does its .align directive.

Differential Revision: http://reviews.llvm.org/D16549

llvm-svn: 258750
diff --git a/llvm/test/CodeGen/ARM/preferred-align.ll b/llvm/test/CodeGen/ARM/preferred-align.ll
index 8cd4ef6..a9a1722 100644
--- a/llvm/test/CodeGen/ARM/preferred-align.ll
+++ b/llvm/test/CodeGen/ARM/preferred-align.ll
@@ -3,19 +3,19 @@
 @var_agg = global {i8, i8} zeroinitializer
 
 ; CHECK: .globl var_agg
-; CHECK-NEXT: .align 2
+; CHECK-NEXT: .p2align 2
 
 @var1 = global i1 zeroinitializer
 
 ; CHECK: .globl var1
-; CHECK-NOT: .align
+; CHECK-NOT: .p2align
 
 @var8 = global i8 zeroinitializer
 
 ; CHECK: .globl var8
-; CHECK-NOT: .align
+; CHECK-NOT: .p2align
 
 @var16 = global i16 zeroinitializer
 
 ; CHECK: .globl var16
-; CHECK-NEXT: .align 1
\ No newline at end of file
+; CHECK-NEXT: .p2align 1
\ No newline at end of file