[CMake] Revive LLVM_*_DIRS variables

This is a partial revert of r280013. Brad King pointed out these variable names are matching CMake conventions, so we should preserve them.

I've also added a direct mapping of the LLVM_*_DIR variables which we need to make projects support building in and out of tree.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280380 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/LLVMConfig.cmake.in

@@ -52,8 +52,15 @@ set(LLVM_ON_WIN32 @LLVM_ON_WIN32@)
 
 set(LLVM_LIBDIR_SUFFIX @LLVM_LIBDIR_SUFFIX@)
 
+set(LLVM_INCLUDE_DIRS "@LLVM_CONFIG_INCLUDE_DIRS@")
+set(LLVM_LIBRARY_DIRS "@LLVM_CONFIG_LIBRARY_DIRS@")
+
+# These variables are duplicated, but they must match the LLVM variables of the
+# same name. The variables ending in "S" could some day become lists, and are
+# preserved for convention and compatibility.
 set(LLVM_INCLUDE_DIR "@LLVM_CONFIG_INCLUDE_DIRS@")
 set(LLVM_LIBRARY_DIR "@LLVM_CONFIG_LIBRARY_DIRS@")
+
 set(LLVM_DEFINITIONS "@LLVM_DEFINITIONS@")
 set(LLVM_CMAKE_DIR "@LLVM_CONFIG_CMAKE_DIR@")
 set(LLVM_BINARY_DIR "@LLVM_CONFIG_BINARY_DIR@")

docs/CMake.rst

@@ -579,7 +579,7 @@ and uses them to build a simple application ``simple-tool``.
   # you will need to enable C++11 support
   # for your compiler.
 
-  include_directories(${LLVM_INCLUDE_DIR})
+  include_directories(${LLVM_INCLUDE_DIRS})
   add_definitions(${LLVM_DEFINITIONS})
 
   # Now build our tools
@@ -636,8 +636,8 @@ include
   This is set to ON if LLVM was built with run time type information (RTTI),
   otherwise OFF.
 
-``LLVM_INCLUDE_DIR``
-  Path to the root directory containing LLVM header files.
+``LLVM_INCLUDE_DIRS``
+  A list of include paths to directories containing LLVM header files.
 
 ``LLVM_PACKAGE_VERSION``
   The LLVM version. This string can be used with CMake conditionals, e.g., ``if
@@ -681,7 +681,7 @@ Contents of ``<project dir>/CMakeLists.txt``:
   find_package(LLVM REQUIRED CONFIG)
 
   add_definitions(${LLVM_DEFINITIONS})
-  include_directories(${LLVM_INCLUDE_DIR})
+  include_directories(${LLVM_INCLUDE_DIRS})
 
   add_subdirectory(<pass name>)