[NDK][NTOS] Add global definition of INIT_FUNCTION/INIT_SECTION (#779)

* Add an NDK header to define INIT_FUNCTION/INIT_SECTION globally
* Use _declspec(allocate(x)) and _declspec(code_seg(x)) on MSVC versions that support it
* Use INIT_FUNCTION on functions only and INIT_SECTION on data only (required by MSVC)
* Place INIT_FUNCTION before the return type (required by MSVC)
* Make sure declarations and implementations share the same modifiers (required by MSVC)
* Add a global linker option to suppress warnings about defined but unused INIT section
* Merge INIT section into .text in freeldr

sdk/include/ndk/section_attribs.h

@@ -0,0 +1,41 @@
+/*++ NDK Version: 0099
+
+Copyright (c) Alex Ionescu.  All rights reserved.
+
+Header Name:
+
+    section_attribs.h
+
+Abstract:
+
+    Preprocessor definitions to put code and data into the INIT section.
+
+Author:
+
+    Timo Kreuzer (timo.kreuzer@reactos.org)
+
+--*/
+
+#pragma once
+
+#ifdef __GNUC__
+
+#define INIT_SECTION  __attribute__((section ("INIT")))
+#define INIT_FUNCTION __attribute__((section ("INIT")))
+
+#elif defined(_MSC_VER)
+
+#pragma comment(linker, "/SECTION:INIT,ERW")
+#define INIT_SECTION  __declspec(allocate("INIT"))
+#if (_MSC_VER >= 1800) // Visual Studio 2013 / version 12.0
+#define INIT_FUNCTION __declspec(code_seg("INIT"))
+#else
+#pragma section("INIT", read,execute,discard)
+#define INIT_FUNCTION
+#endif
+
+#else
+
+#error Invalid compiler!
+
+#endif