Don't drop alignment info on local common symbols.

- On COFF the .lcomm directive has an alignment argument.
- On ELF we fall back to .local + .comm

Based on a patch by NAKAMURA Takumi.

Fixes PR9337, PR9483 and PR10128.

llvm-svn: 138976
diff --git a/llvm/test/CodeGen/ARM/elf-lcomm-align.ll b/llvm/test/CodeGen/ARM/elf-lcomm-align.ll
new file mode 100644
index 0000000..4679299
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/elf-lcomm-align.ll
@@ -0,0 +1,14 @@
+; RUN: llc < %s -mtriple=arm-linux-gnueabi -O0 | FileCheck %s
+; run with -O0 to avoid arm global merging.
+
+@c = internal global i8 0, align 1
+@x = internal global i32 0, align 4
+
+; CHECK: .lcomm c,1
+; .lcomm doesn't support alignment.
+; CHECK: .local x
+; CHECK-NEXT: .comm x,4,4
+
+define i32 @foo() nounwind {
+  ret i32 sub (i32 ptrtoint (i8* @c to i32), i32 ptrtoint (i32* @x to i32))
+}