[MIR] Add support for debug metadata for fixed stack objects

Debug var, expr and loc were only supported for non-fixed stack objects.

This patch adds the following fields to the "fixedStack:" entries, and
renames the ones from "stack:" to:

* debug-info-variable
* debug-info-expression
* debug-info-location

Differential Revision: https://reviews.llvm.org/D46032

llvm-svn: 330859
diff --git a/llvm/test/CodeGen/MIR/X86/stack-object-debug-info.mir b/llvm/test/CodeGen/MIR/X86/stack-object-debug-info.mir
index 554d73b..bfaf8a4 100644
--- a/llvm/test/CodeGen/MIR/X86/stack-object-debug-info.mir
+++ b/llvm/test/CodeGen/MIR/X86/stack-object-debug-info.mir
@@ -52,10 +52,12 @@
 # CHECK: stack:
 # CHECK:  - { id: 0, name: y.i, type: default, offset: 0, size: 256, alignment: 16,
 # CHECK-NEXT: callee-saved-register: '', callee-saved-restored: true,
-# CHECK-NEXT: di-variable: '!4', di-expression: '!DIExpression()', di-location: '!10' }
+# CHECK-NEXT: debug-info-variable: '!4', debug-info-expression: '!DIExpression()',
+# CHECK-NEXT: debug-info-location: '!10' }
 stack:
-  - { id: 0, name: y.i, offset: 0, size: 256, alignment: 16, di-variable: '!4',
-      di-expression: '!DIExpression()', di-location: '!7' }
+  - { id: 0, name: y.i, offset: 0, size: 256, alignment: 16,
+      debug-info-variable: '!4', debug-info-expression: '!DIExpression()',
+      debug-info-location: '!7' }
 body: |
   bb.0.entry:
     successors: %bb.1.for.body