`libqcdm`'s meson build files have been improved slightly by
removing unnecessary variables shortening their contents.

meson is a build system focused on speed an ease of use, which
helps speeding up the software development. This patch adds meson
support along autotools.

  reset.c: In function ‘main’:
  reset.c:238:17: warning: passing argument 1 of ‘putenv’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    238 |         putenv ("QCDM_DEBUG=1");
        |                 ^~~~~~~~~~~~~~
  In file included from reset.c:22:
  /usr/include/stdlib.h:647:26: note: expected ‘char *’ but argument is of type ‘const char *’
    647 | extern int putenv (char *__string) __THROW __nonnull ((1));
        |                    ~~~~~~^~~~~~~~

  reset.c: In function ‘print_buf’:
  reset.c:47:19: warning: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
     47 |     for (i = 0; i < len; i++) {
        |                   ^
  reset.c: In function ‘qcdm_wait_reply’:
  reset.c:168:20: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
    168 |     } while (total < sizeof (readbuf));
        |                    ^

  ipv6pref.c: In function ‘main’:
  ipv6pref.c:288:11: warning: passing argument 1 of ‘putenv’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    288 |   putenv ("QCDM_DEBUG=1");
        |           ^~~~~~~~~~~~~~

  ipv6pref.c: In function ‘print_buf’:
  ipv6pref.c:46:16: warning: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
     46 |  for (i = 0; i < len; i++) {
        |                ^
  ipv6pref.c: In function ‘qcdm_wait_reply’:
  ipv6pref.c:167:17: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
    167 |  } while (total < sizeof (readbuf));
        |                 ^

  modepref.c: In function ‘main’:
  modepref.c:539:11: warning: passing argument 1 of ‘putenv’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    539 |   putenv ("QCDM_DEBUG=1");
        |           ^~~~~~~~~~~~~~
  In file included from modepref.c:21:
  /usr/include/stdlib.h:647:26: note: expected ‘char *’ but argument is of type ‘const char *’
    647 | extern int putenv (char *__string) __THROW __nonnull ((1));
        |                    ~~~~~~^~~~~~~~

  modepref.c: In function ‘print_buf’:
  modepref.c:46:16: warning: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
     46 |  for (i = 0; i < len; i++) {
        |                ^
  modepref.c: In function ‘qcdm_wait_reply’:
  modepref.c:167:17: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
    167 |  } while (total < sizeof (readbuf));
        |                 ^

  test-qcdm-com.c: In function ‘test_com_pilot_sets’:
  test-qcdm-com.c:1085:59: warning: implicit conversion from ‘float’ to ‘double’ when passing argument to function [-Wdouble-promotion]
   1085 |         g_message ("      EC/IO     %d  (%.1f dB)", ecio, db);
        |                                                           ^~
  /usr/include/glib-2.0/glib/gmessages.h:333:32: note: in definition of macro ‘g_message’
    333 |                                __VA_ARGS__)
        |                                ^~~~~~~~~~~