add gfx2mem.c/.h: GFX2_malloc() to log allocation failures

src/gfx2mem.h

@@ -0,0 +1,30 @@
+/* vim:expandtab:ts=2 sw=2:
+*/
+/*  Grafx2 - The Ultimate 256-color bitmap paint program
+
+    Copyright 2019 Thomas Bernard
+    Copyright 1996-2001 Sunset Design (Guillaume Dorme & Karl Maritaud)
+
+    Grafx2 is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation; version 2
+    of the License.
+
+    Grafx2 is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Grafx2; if not, see <http://www.gnu.org/licenses/>
+*/
+#ifndef GFX2MEM_H_DEFINED
+#define GFX2MEM_H_DEFINED
+
+/// malloc() memory and log in case of error
+void * GFX2_malloc_and_log(size_t size, const char * file, unsigned line);
+
+/// malloc() memory and log in case of error
+#define GFX2_malloc(size) GFX2_malloc_and_log((size), __FILE__, __LINE__)
+
+#endif