meson: link with libm for math functions

Fixes this error I got building on F33:
  /usr/bin/ld: test-random-util.p/src_test_test-random-util.c.o: undefined
  reference to symbol 'sqrt@@GLIBC_2.2.5'
  /usr/bin/ld: /usr/lib64/libm.so.6: error adding symbols: DSO missing
  from command line

src/test/meson.build

@@ -158,7 +158,9 @@ tests += [
 
         [['src/test/test-fstab-util.c']],
 
-        [['src/test/test-random-util.c']],
+        [['src/test/test-random-util.c'],
+         [],
+         [libm]],
 
         [['src/test/test-format-table.c']],