[machdep] more robust generator

- --compile-flags="-c -I/path" works (i.e. there's no need to provide as many
  --compile-flags options as you have flags to pass to the compiler itself.
  Ditto for --cpp-arch-flags of course
- we start by checking that a minimal C file does not trigger a compiler error
  with the given option and we abort otherwise. This ensures that subsequent
  tests will not mistakenly take a configuration error for a genuine result.

share/machdeps/make_machdep/make_machdep.py

@@ -176,9 +176,15 @@ def make_machdep():
 
 machdep = make_machdep()
 
-compilation_command = [args.compiler] + args.cpp_arch_flags + args.compiler_flags
+compilation_command = [args.compiler]
+
+for flag in args.cpp_arch_flags + args.compiler_flags:
+    compilation_command = compilation_command + flag.split(" ")
 
 source_files = [
+    # sanity_check is juste here to ensure that the given compiler
+    # and flags are coherent. It must be kept at the top of the list.
+    ("sanity_check.c", "none"),
     ("sizeof_short.c", "number"),
     ("sizeof_int.c", "number"),
     ("sizeof_long.c", "number"),
@@ -317,6 +323,12 @@ for f, typ in source_files:
         print(f"[INFO] running command: {' '.join(cmd)}")
     proc = subprocess.run(cmd, capture_output=True)
     Path(f).with_suffix(".o").unlink(missing_ok=True)
+    if typ == "none":
+        if proc.returncode != 0:
+            logging.critical("cannot compile sample C file with provided compiler and flags.")
+            logging.info(f"compiler output is:{proc.stderr.decode()}")
+            sys.exit(1)
+        continue
     if typ == "macro":
         if proc.returncode != 0:
             logging.warning(f"error in preprocessing value '{p}', some values won't be filled")

share/machdeps/make_machdep/sanity_check.c

+/**************************************************************************/
+/*                                                                        */
+/*  This file is part of Frama-C.                                         */
+/*                                                                        */
+/*  Copyright (C) 2007-2023                                               */
+/*    CEA (Commissariat à l'énergie atomique et aux énergies              */
+/*         alternatives)                                                  */
+/*                                                                        */
+/*  you can redistribute it and/or modify it under the terms of the GNU   */
+/*  Lesser General Public License as published by the Free Software       */
+/*  Foundation, version 2.1.                                              */
+/*                                                                        */
+/*  It 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 Lesser General Public License for more details.                   */
+/*                                                                        */
+/*  See the GNU Lesser General Public License version 2.1                 */
+/*  for more details (enclosed in the file licenses/LGPLv2.1).            */
+/*                                                                        */
+/**************************************************************************/
+
+/* ensure that the given compiler and flags support a minimal C file */
+int main () { }