compilers: avoid -Wunused-value compiler warning in CLikeCompiler.has_members()

Otherwise, `CFLAGS='-Wall -Werror' meson build` can fail detection:

          void bar(void) {
              struct stat foo;
              foo.st_mtim.tv_nsec;

          }
  -----------
  Command line: `cc ./project/build/meson-private/tmpqz_gi65d/testfile.c -o ./project/build/meson-private/tmpqz_gi65d/output.obj -c -O3 -Werror -Wall -D_FILE_OFFSET_BITS=64 -O0 -std=gnu99` -> 1
  stderr:
  ./project/build/meson-private/tmpqz_gi65d/testfile.c: In function 'bar':
  ./project/build/meson-private/tmpqz_gi65d/testfile.c:45:24: error: statement with no effect [-Werror=unused-value]
     45 |             foo.st_mtim.tv_nsec;
        |             ~~~~~~~~~~~^~~~~~~~
  cc1: all warnings being treated as errors

0 files changed, 0 insertions, 0 deletions