[llvm-c] Add LLVMPointerType2

[aeubanks]

Summary

In preparation for removing some of the typed pointer APIs.

[nikic]

Do we really need this? I thought we intentionally don't add more APIs using the global context.

[aeubanks]

In D145712#4182339, @nikic wrote:

Do we really need this? I thought we intentionally don't add more APIs using the global context.

I wasn't aware of that, I can abandon this patch if so

llvm/docs/ReleaseNotes.rst

 --------------------
 
 * ``LLVMContextSetOpaquePointers``, a temporary API to pin to legacy typed
   pointer, has been removed.
 * Functions for adding legacy passes like ``LLVMAddInstructionCombiningPass``
   have been removed.
 * Removed ``LLVMPassManagerBuilderRef`` and functions interacting with it.
   These belonged to the no longer supported legacy pass manager.
+* Added the convenience ``LLVMPointerType2`` function to create an opaque
+  pointer in the global context.
 
 Changes to the FastISel infrastructure
 --------------------------------------
 
 * ...
 
 Changes to the DAG infrastructure
 ---------------------------------

llvm/include/llvm-c/Core.h

  * The created type will exist in the context that its pointee type
  * exists in.
  *
  * @see llvm::PointerType::get()
  */
 LLVMTypeRef LLVMPointerType(LLVMTypeRef ElementType, unsigned AddressSpace);
 
 /**
+ * Create an opaque pointer type in the global context.
+ *
+ * @see llvm::PointerType::get()
+ */
+LLVMTypeRef LLVMPointerType2(unsigned AddressSpace);
+
+/**
  * Determine whether a pointer is opaque.
  *
  * True if this is an instance of an opaque PointerType.
  *
  * @see llvm::Type::isOpaquePointerTy()
  */
 LLVMBool LLVMPointerTypeIsOpaque(LLVMTypeRef Ty);
 

llvm/lib/IR/Core.cpp

 }
 LLVMTypeRef LLVMTokenTypeInContext(LLVMContextRef C) {
   return wrap(Type::getTokenTy(*unwrap(C)));
 }
 LLVMTypeRef LLVMMetadataTypeInContext(LLVMContextRef C) {
   return wrap(Type::getMetadataTy(*unwrap(C)));
 }
 
+LLVMTypeRef LLVMPointerType2(unsigned AddressSpace) {
+  return LLVMPointerTypeInContext(LLVMGetGlobalContext(), AddressSpace);
+}
 LLVMTypeRef LLVMVoidType(void)  {
   return LLVMVoidTypeInContext(LLVMGetGlobalContext());
 }
 LLVMTypeRef LLVMLabelType(void) {
   return LLVMLabelTypeInContext(LLVMGetGlobalContext());
 }
 
 LLVMTypeRef LLVMTargetExtTypeInContext(LLVMContextRef C, const char *Name,