[HIPIFY][fix][#211] Taking into account include guard controlling macro

...while including HIP main header file, which is inserted now after #indef controlling macro, or after #pragma once, if it's occurred earlier.

+ Add a couple of unit tests.
ToDo: Check backward compatibility on older clang versions.

tests/hipify-clang/unit_tests/headers/headers_test_10.cu

@@ -0,0 +1,14 @@
+// RUN: %run_test hipify "%s" "%t" %hipify_args %clang_args
+
+// Checks that HIP header file is included after #pragma once,
+// which goes before include guard controlling macro.
+// CHECK: #pragma once
+// CHECK-NEXT: #include <hip/hip_runtime.h>
+#pragma once
+#ifndef HEADERS_TEST_10_H
+// CHECK: #ifndef HEADERS_TEST_10_H
+// CHECK-NOT: #include <hip/hip_runtime.h>
+#define HEADERS_TEST_10_H
+#include <stdio.h>
+static int counter = 0;
+#endif // HEADERS_TEST_10_H

tests/hipify-clang/unit_tests/headers/headers_test_11.cu

@@ -0,0 +1,14 @@
+// RUN: %run_test hipify "%s" "%t" %hipify_args %clang_args
+
+// Checks that HIP header file is included after include guard controlling macro,
+// which goes before #pragma once.
+// CHECK: #ifndef HEADERS_TEST_10_H
+// CHECK-NEXT: #include <hip/hip_runtime.h>
+#ifndef HEADERS_TEST_10_H
+// CHECK: #pragma once
+#pragma once
+// CHECK-NOT: #include <hip/hip_runtime.h>
+#define HEADERS_TEST_10_H
+#include <stdio.h>
+static int counter = 0;
+#endif // HEADERS_TEST_10_H