Allow making reference to global variables.

Sources/LLVM/IRBuilder.swift

@@ -108,6 +108,43 @@ public enum RealPredicate {
   }
 }
 
+extension Module {
+  /// Searches for and retrieves a global variable with the given name in this 
+  /// module if that name references an existing global variable.
+  ///
+  /// - parameter name: The name of the global to reference.
+  ///
+  /// - returns: A value representing the referenced global if it exists.
+  public func global(named name: String) -> Global? {
+    guard let ref = LLVMGetNamedGlobal(llvm, name) else { return nil }
+    return Global(llvm: ref)
+  }
+
+  /// Searches for and retrieves a type with the given name in this module if
+  /// that name references an existing type.
+  ///
+  /// - parameter name: The name of the type to create.
+  ///
+  /// - returns: A representation of the newly created type with the given name
+  ///   or nil if such a representation could not be created.
+  public func type(named name: String) -> IRType? {
+    guard let type = LLVMGetTypeByName(llvm, name) else { return nil }
+    return convertType(type)
+  }
+
+  /// Searches for and retrieves a function with the given name in this module
+  /// if that name references an existing function.
+  ///
+  /// - parameter name: The name of the function to create.
+  ///
+  /// - returns: A representation of the newly created function with the given
+  /// name or nil if such a representation could not be created.
+  public func function(named name: String) -> Function? {
+    guard let fn = LLVMGetNamedFunction(llvm, name) else { return nil }
+    return Function(llvm: fn)
+  }
+}
+
 /// An `IRBuilder` is a helper object that generates LLVM instructions.  IR 
 /// Builders keep track of a position within a function or basic block and has
 /// methods to insert instructions at that position.
@@ -935,7 +972,7 @@ public class IRBuilder {
     return LLVMBuildInsertElement(llvm, vector.asLLVM(), element.asLLVM(), index.asLLVM(), name)
   }
 
-  // MARK: Global Variable Creation Instructions
+  // MARK: Global Variable Instructions
 
   /// Build a named global of the given type.
   ///
@@ -974,8 +1011,8 @@ public class IRBuilder {
   /// - parameter name: The name for the newly inserted instruction.
   ///
   /// - returns: A value representing the newly inserted global string variable.
-  public func buildGlobalString(_ string: String, name: String = "") -> IRValue {
-    return LLVMBuildGlobalString(llvm, string, name)
+  public func buildGlobalString(_ string: String, name: String = "") -> Global {
+    return Global(llvm: LLVMBuildGlobalString(llvm, string, name))
   }
 
   /// Builds a named global variable containing a pointer to the contents of the

Sources/LLVM/Module.swift

@@ -110,30 +110,6 @@ public final class Module {
     }
   }
 
-  /// Searches for and retrieves a type with the given name in this module if
-  /// that name references an existing type.
-  ///
-  /// - parameter name: The name of the type to create.
-  ///
-  /// - returns: A representation of the newly created type with the given name
-  ///   or nil if such a representation could not be created.
-  public func type(named name: String) -> IRType? {
-    guard let type = LLVMGetTypeByName(llvm, name) else { return nil }
-    return convertType(type)
-  }
-
-  /// Searches for and retrieves a function with the given name in this module
-  /// if that name references an existing function.
-  ///
-  /// - parameter name: The name of the function to create.
-  ///
-  /// - returns: A representation of the newly created function with the given
-  /// name or nil if such a representation could not be created.
-  public func function(named name: String) -> Function? {
-    guard let fn = LLVMGetNamedFunction(llvm, name) else { return nil }
-    return Function(llvm: fn)
-  }
-
   /// Verifies that this module is valid, taking the specified action if not.
   /// If this module did not pass verification, a description of any invalid
   /// constructs is provided with the thrown