meson: avoid unused arguments of main() in compiler tests

meson.build has one test where "main" is declared unnecessarily
with argc and argv arguments, but does not use them.  Because
the test needs -Werror too, HAVE_BROKEN_SIZE_MAX is defined
incorrectly.

Fix the test and, for consistency, remove argc and argv whenever
they are not needed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -2165,7 +2165,7 @@ config_host_data.set('CONFIG_SPLICE', cc.links(gnu_source_prefix + '''
 
 config_host_data.set('HAVE_MLOCKALL', cc.links(gnu_source_prefix + '''
   #include <sys/mman.h>
-  int main(int argc, char *argv[]) {
+  int main(void) {
     return mlockall(MCL_FUTURE);
   }'''))
 
@@ -2210,7 +2210,7 @@ config_host_data.set('HAVE_FSXATTR', cc.links('''
 config_host_data.set('HAVE_BROKEN_SIZE_MAX', not cc.compiles('''
     #include <stdint.h>
     #include <stdio.h>
-    int main(int argc, char *argv[]) {
+    int main(void) {
         return printf("%zu", SIZE_MAX);
     }''', args: ['-Werror']))
 
@@ -2327,7 +2327,7 @@ config_host_data.set('CONFIG_AVX2_OPT', get_option('avx2') \
       __m256i x = *(__m256i *)a;
       return _mm256_testz_si256(x, x);
     }
-    int main(int argc, char *argv[]) { return bar(argv[0]); }
+    int main(int argc, char *argv[]) { return bar(argv[argc - 1]); }
   '''), error_message: 'AVX2 not available').allowed())
 
 config_host_data.set('CONFIG_AVX512F_OPT', get_option('avx512f') \
@@ -2341,7 +2341,7 @@ config_host_data.set('CONFIG_AVX512F_OPT', get_option('avx512f') \
       __m512i x = *(__m512i *)a;
       return _mm512_test_epi64_mask(x, x);
     }
-    int main(int argc, char *argv[]) { return bar(argv[0]); }
+    int main(int argc, char *argv[]) { return bar(argv[argc - 1]); }
   '''), error_message: 'AVX512F not available').allowed())
 
 have_pvrdma = get_option('pvrdma') \