[llvm] include Compiler.h in a few headers where it was missed (#144464)

Add missing `#include "llvm/Support/Compiler.h"` in a few LLVM headers
that use the `LLVM_ABI` macro.

Author: andrurogerz

llvm/include/llvm/Option/OptSpecifier.h

@@ -9,6 +9,8 @@
 #ifndef LLVM_OPTION_OPTSPECIFIER_H
 #define LLVM_OPTION_OPTSPECIFIER_H
 
+#include "llvm/Support/Compiler.h"
+
 namespace llvm {
 namespace opt {
 

llvm/include/llvm/Transforms/IPO.h

@@ -14,6 +14,8 @@
 #ifndef LLVM_TRANSFORMS_IPO_H
 #define LLVM_TRANSFORMS_IPO_H
 
+#include "llvm/Support/Compiler.h"
+
 namespace llvm {
 
 class ModulePass;

llvm/include/llvm/Transforms/Utils/PromoteMemToReg.h

@@ -14,6 +14,8 @@
 #ifndef LLVM_TRANSFORMS_UTILS_PROMOTEMEMTOREG_H
 #define LLVM_TRANSFORMS_UTILS_PROMOTEMEMTOREG_H
 
+#include "llvm/Support/Compiler.h"
+
 namespace llvm {
 
 template <typename T> class ArrayRef;