cleanup: fix compile warnings associated with gnu_printf

[bandoti]

Various warnings occur (of the form below) due to no defined gnu_printf on clang with MSYS2. In addition, a couple printfs have superfluous %s in the format string. Both of these issues are cleaned up in this PR.

In file included from ...include/llama.h:4:
...include/ggml.h:317:19: warning: 'format' attribute argument not supported: gnu_printf [-Wignored-
attributes]
  317 |     GGML_NORETURN GGML_ATTRIBUTE_FORMAT(3, 4)
      |                   ^
...include/ggml.h:202:55: note: expanded from macro 'GGML_ATTRIBUTE_FORMAT'
  202 | #    define GGML_ATTRIBUTE_FORMAT(...) __attribute__((format(gnu_printf, __VA_ARGS__)))
      |                                                       ^
...include/ggml.h:760:5: warning: 'format' attribute argument not supported: gnu_printf [-Wignored-a
ttributes]
  760 |     GGML_ATTRIBUTE_FORMAT(2, 3)

[ggerganov]

I'm not sure about the !defined(__clang__) changes, so better wait for someone to confirm.