[ORC-RT] Make the ORC runtime C API public.

This is a first step towards allowing programs to pre-link against the ORC
runtime, which would allow us to move some code that is currently in the LLVM
OrcTarget library into the ORC runtime instead.

The C API header has limited utility as-is, but serves as a minimal first step
and provides clients with tools for interacting with wrapper functions.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D127324

compiler-rt/lib/orc/wrapper_function_utils.h

@@ -13,7 +13,7 @@
 #ifndef ORC_RT_WRAPPER_FUNCTION_UTILS_H
 #define ORC_RT_WRAPPER_FUNCTION_UTILS_H
 
-#include "c_api.h"
+#include "orc/c_api.h"
 #include "common.h"
 #include "error.h"
 #include "executor_address.h"