Fix for zero length array warning and gcc

[garth-wells]

GCC doesn't have "-Wzero-length-array" (unlike clang) [1], which caused #345. This change allows -Werror -pedantic builds with GCC and clang.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94428

[wjakob]

Sorry, I really don't like this change. You could alternatively realize it in your project by putting those pragmas around

#include <nanobind/nanobind.h>