Add explicit link targets to some headers in LangRef.rst

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183548 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -387,6 +387,8 @@ More calling conventions can be added/defined on an as-needed basis, to
 support Pascal conventions or any other well-known target-independent
 convention.
 
+.. _visibilitystyles:
+
 Visibility Styles
 -----------------
 
@@ -412,6 +414,8 @@ styles:
     defining module will bind to the local symbol. That is, the symbol
     cannot be overridden by another module.
 
+.. _namedtypes:
+
 Named Types
 -----------
 
@@ -596,6 +600,8 @@ Syntax::
            [fn Attrs] [section "name"] [align N]
            [gc] { ... }
 
+.. _langref_aliases:
+
 Aliases
 -------
 
@@ -970,6 +976,8 @@ two digit hex code for the number.
 The inline asm code is simply printed to the machine code .s file when
 assembly code is generated.
 
+.. _langref_datalayout:
+
 Data Layout
 -----------