Revert "[IR] Remove the DIExpression field from DIGlobalVariable."

This reverts commit 289920 (again).
I forgot to implement a Bitcode upgrade for the case where a DIGlobalVariable
has not DIExpression. Unfortunately it is not possible to safely upgrade
these variables without adding a flag to the bitcode record indicating which
version they are.
My plan of record is to roll the planned follow-up patch that adds a
unit: field to DIGlobalVariable into this patch before recomitting.
This way we only need one Bitcode upgrade for both changes (with a
version flag in the bitcode record to safely distinguish the record
formats).

Sorry for the churn!

llvm-svn: 289982
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 712a2c6..d4de28e 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -4197,7 +4197,8 @@
 /// ParseDIGlobalVariable:
 ///   ::= !DIGlobalVariable(scope: !0, name: "foo", linkageName: "foo",
 ///                         file: !1, line: 7, type: !2, isLocal: false,
-///                         isDefinition: true, declaration: !3, align: 8)
+///                         isDefinition: true, variable: i32* @foo,
+///                         declaration: !3, align: 8)
 bool LLParser::ParseDIGlobalVariable(MDNode *&Result, bool IsDistinct) {
 #define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
   REQUIRED(name, MDStringField, (/* AllowEmpty */ false));                     \
@@ -4208,6 +4209,7 @@
   OPTIONAL(type, MDField, );                                                   \
   OPTIONAL(isLocal, MDBoolField, );                                            \
   OPTIONAL(isDefinition, MDBoolField, (true));                                 \
+  OPTIONAL(expr, MDField, );                                                   \
   OPTIONAL(declaration, MDField, );                                            \
   OPTIONAL(align, MDUnsignedField, (0, UINT32_MAX));
   PARSE_MD_FIELDS();
@@ -4216,7 +4218,8 @@
   Result = GET_OR_DISTINCT(DIGlobalVariable,
                            (Context, scope.Val, name.Val, linkageName.Val,
                             file.Val, line.Val, type.Val, isLocal.Val,
-                            isDefinition.Val, declaration.Val, align.Val));
+                            isDefinition.Val, expr.Val, declaration.Val,
+                            align.Val));
   return false;
 }
 
@@ -4284,21 +4287,6 @@
   return false;
 }
 
-/// ParseDIGlobalVariableExpression:
-///   ::= !DIGlobalVariableExpression(var: !0, expr: !1)
-bool LLParser::ParseDIGlobalVariableExpression(MDNode *&Result,
-                                               bool IsDistinct) {
-#define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
-  REQUIRED(var, MDField, );                                                    \
-  OPTIONAL(expr, MDField, );
-  PARSE_MD_FIELDS();
-#undef VISIT_MD_FIELDS
-
-  Result =
-      GET_OR_DISTINCT(DIGlobalVariableExpression, (Context, var.Val, expr.Val));
-  return false;
-}
-
 /// ParseDIObjCProperty:
 ///   ::= !DIObjCProperty(name: "foo", file: !1, line: 7, setter: "setFoo",
 ///                       getter: "getFoo", attributes: 7, type: !2)