sandbox/bugs/qcc-is_code

When qcc is compiled in a directory containing “.c” or “.h”, qcc no longer is able to correctly compile Basilisk C code files.

To reproduce the bug:

1. Clone basilisk into /tmp/foo.h.bar/ or /tmp/foo.c.bar/
2. Compile all targets as normal in the makefile build system, which sets -DBASILISK="/tmp/foo.h.bar/src" when compiling qcc
3. Attempt to compile any basilisk code example, such as karman.c using /tmp/foo.h.bar/src/qcc karman.c.

The cause has to due with the use of strstr in is_code in include.lex.

Redefining the function as follows resolves the issue

static int is_code (const char * file)
{
  // check whether the basename has a .c or .h extension
  const char * base = strrchr (file, '/');
  base = base ? base + 1 : file;
  const char * s = strrchr (base, '.');
  return s && (!strcmp (s, ".c") || !strcmp (s, ".h"));
}