allocators: move standard allocator into subdirectory

Right now, our two allocator implementations are scattered around
the tree in "stdalloc.h" and "win32/w32_crtdbg_stacktrace.h".
Start grouping them together in a single directory "allocators/",
similar to how e.g. our streams are organized.

src/CMakeLists.txt

@@ -428,6 +428,7 @@ ELSE()
 	FILE(GLOB SRC_OS unix/*.c unix/*.h)
 ENDIF()
 FILE(GLOB SRC_GIT2 *.c *.h
+	allocators/*.c allocators/*.h
 	streams/*.c streams/*.h
 	transports/*.c transports/*.h
 	xdiff/*.c xdiff/*.h)

src/alloc.c

@@ -10,7 +10,7 @@
 #if defined(GIT_MSVC_CRTDBG)
 # include "win32/w32_crtdbg_stacktrace.h"
 #else
-# include "stdalloc.h"
+# include "allocators/stdalloc.h"
 #endif
 
 git_allocator git__allocator;

src/stdalloc.h → src/allocators/stdalloc.h

@@ -5,13 +5,13 @@
  * a Linking Exception. For full terms see the included COPYING file.
  */
 
-#ifndef INCLUDE_stdalloc_h__
-#define INCLUDE_stdalloc_h__
-
-#include "alloc.h"
+#ifndef INCLUDE_allocators_stdalloc_h__
+#define INCLUDE_allocators_stdalloc_h__
 
 #include "common.h"
 
+#include "alloc.h"
+
 int git_stdalloc_init_allocator(git_allocator *allocator);
 
 #endif