new configure option: NOT_FOR_DISTRIBUTION

fix safemalloc to compile w/o libbfd.

CMakeLists.txt:
  NOT_FOR_DISTRIBUTION option
cmake/readline.cmake:
  simplify libedit/readline detection.
  never use bundled libedit.
  use system readline v6 only if NOT_FOR_DISTRIBUTION=1
configure.cmake:
  use libbfd only if NOT_FOR_DISTRIBUTION=1
include/my_stacktrace.h:
  link with libbfd even w/o safemalloc.

mysys/my_addr_resolve.c

@@ -21,6 +21,7 @@
 /**
   strip the path, leave the file name and the last dirname
 */
+static const char *strip_path(const char *s) __attribute__((unused));
 static const char *strip_path(const char *s)
 {
   const char *prev, *last;