readline fails to build on MacOS

[j2kun]

From google/heir#2282

external/org_gnu_readline/xmalloc.h:41:30: error: a parameter list without types is only allowed in a function definition
   41 | extern PTR_T xmalloc PARAMS((size_t));
      |                              ^
external/org_gnu_readline/xmalloc.h:42:39: error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
   42 | extern PTR_T xrealloc PARAMS((void *, size_t));
      |                                       ^
      |                                       int
external/org_gnu_readline/rlstdc.h:33:28: note: expanded from macro 'PARAMS'
   33 | #    define PARAMS(protos) protos