cmake: Remove add_llvm_loadable_module()

Summary:
This function is very similar to add_llvm_library(),  so this patch merges it
into add_llvm_library() and replaces all calls to add_llvm_loadable_module(lib ...)
with add_llvm_library(lib MODULE ...)

Reviewers: philip.pfaffe, beanz, chandlerc

Reviewed By: philip.pfaffe

Subscribers: chapuni, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D51748

llvm-svn: 349839
diff --git a/llvm/docs/CMake.rst b/llvm/docs/CMake.rst
index f4f67db..d27c0a8 100644
--- a/llvm/docs/CMake.rst
+++ b/llvm/docs/CMake.rst
@@ -774,7 +774,7 @@
 
 Note if you intend for this pass to be merged into the LLVM source tree at some
 point in the future it might make more sense to use LLVM's internal
-``add_llvm_loadable_module`` function instead by...
+``add_llvm_library`` function with he MODULE argument instead by...
 
 
 Adding the following to ``<project dir>/CMakeLists.txt`` (after
@@ -789,7 +789,7 @@
 
 .. code-block:: cmake
 
-  add_llvm_loadable_module(LLVMPassname
+  add_llvm_library(LLVMPassname MODULE
     Pass.cpp
     )