consider enabling -Wextra

[nathanlynch]

GCC 11 manual says -Wextra enables:

          -Wclobbered
          -Wcast-function-type
          -Wdeprecated-copy (C++ only)
          -Wempty-body
          -Wenum-conversion (C only)
          -Wignored-qualifiers
          -Wimplicit-fallthrough=3
          -Wmissing-field-initializers
          -Wmissing-parameter-type (C only)
          -Wold-style-declaration (C only)
          -Woverride-init
          -Wsign-compare (C only)
          -Wstring-compare
          -Wredundant-move (only for C++)
          -Wtype-limits
          -Wuninitialized
          -Wshift-negative-value (in C++03 and in C99 and newer)
          -Wunused-parameter (only with -Wunused or -Wall)
          -Wunused-but-set-parameter (only with -Wunused or -Wall)

Adding it to the build yields:

  CC       librtas_src/ofdt.lo
  CC       librtas_src/syscall_calls.lo
librtas_src/syscall_calls.c: In function ‘rtas_physical_attestation’:
librtas_src/syscall_calls.c:1381:33: warning: comparison of integer expressions of different signedness: ‘__uint32_t’ {aka ‘unsigned int’} and ‘int’ [-Wsign-compare]
 1381 |         if (be32toh(resp_bytes) > *work_area_bytes) {
      |                                 ^
  CC       librtas_src/syscall_rmo.lo
librtas_src/syscall_rmo.c: In function ‘get_phys_region’:
librtas_src/syscall_rmo.c:243:37: warning: comparison of integer expressions of different signedness: ‘int’ and ‘uint32_t’ {aka ‘unsigned int’} [-Wsign-compare]
  243 |                 if ((i * PAGE_SIZE) >= kregion->size)
      |                                     ^~
librtas_src/syscall_rmo.c: In function ‘release_phys_region’:
librtas_src/syscall_rmo.c:292:18: warning: comparison of integer expressions of different signedness: ‘uint64_t’ {aka ‘long unsigned int’} and ‘int’ [-Wsign-compare]
  292 |         if (bits != ((1 << n_pages) - 1)) {
      |                  ^~
  CCLD     librtas.la
  CC       librtasevent_src/get_rtas_event.lo
librtasevent_src/get_rtas_event.c: In function ‘parse_rtas_event’:
librtasevent_src/get_rtas_event.c:411:26: warning: comparison of integer expressions of different signedness: ‘uint32_t’ {aka ‘unsigned int’} and ‘int’ [-Wsign-compare]
  411 |     if (re->event_length > buflen) {
      |                          ^
  CC       librtasevent_src/print_rtas_event.lo
librtasevent_src/print_rtas_event.c: In function ‘print_re_exthdr_scn’:
librtasevent_src/print_rtas_event.c:542:50: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
  542 | print_re_exthdr_scn(struct scn_header *shdr, int verbosity)
      |                                              ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_cpu.lo
librtasevent_src/rtas_cpu.c: In function ‘print_re_cpu_scn’:
librtasevent_src/rtas_cpu.c:82:47: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   82 | print_re_cpu_scn(struct scn_header *shdr, int verbosity)
      |                                           ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_dump.lo
  CC       librtasevent_src/rtas_epow.lo
librtasevent_src/rtas_epow.c: In function ‘print_v4_epow’:
librtasevent_src/rtas_epow.c:95:44: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   95 | print_v4_epow(struct scn_header *shdr, int verbosity)
      |                                        ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_io.lo
librtasevent_src/rtas_io.c: In function ‘print_v4_io’:
librtasevent_src/rtas_io.c:97:42: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   97 | print_v4_io(struct scn_header *shdr, int verbosity)
      |                                      ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_lri.lo
  CC       librtasevent_src/rtas_mem.lo
librtasevent_src/rtas_mem.c: In function ‘print_re_mem_scn’:
librtasevent_src/rtas_mem.c:78:47: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   78 | print_re_mem_scn(struct scn_header *shdr, int verbosity)
      |                                           ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_post.lo
librtasevent_src/rtas_post.c: In function ‘print_re_post_scn’:
librtasevent_src/rtas_post.c:93:48: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   93 | print_re_post_scn(struct scn_header *shdr, int verbosity)
      |                                            ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_sp.lo
librtasevent_src/rtas_sp.c: In function ‘print_re_ibmsp_scn’:
librtasevent_src/rtas_sp.c:78:49: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   78 | print_re_ibmsp_scn(struct scn_header *shdr, int verbosity)
      |                                             ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_srcfru.lo
librtasevent_src/rtas_srcfru.c: In function ‘print_fru_mr_scn’:
librtasevent_src/rtas_srcfru.c:518:19: warning: comparison of integer expressions of different signedness: ‘int’ and ‘uint32_t’ {aka ‘unsigned int’} [-Wsign-compare]
  518 |     for (i = 0; i < frumr_num_callouts(fru_mr); i++) {
      |                   ^
  CC       librtasevent_src/rtas_v6_misc.lo
librtasevent_src/rtas_v6_misc.c: In function ‘print_re_generic_scn’:
librtasevent_src/rtas_v6_misc.c:674:51: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
  674 | print_re_generic_scn(struct scn_header *shdr, int verbosity)
      |                                               ~~~~^~~~~~~~~
  CC       librtasevent_src/rtas_vend.lo
librtasevent_src/rtas_vend.c: In function ‘print_re_ibm_diag_scn’:
librtasevent_src/rtas_vend.c:77:52: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
   77 | print_re_ibm_diag_scn(struct scn_header *shdr, int verbosity)
      |                                                ~~~~^~~~~~~~~
librtasevent_src/rtas_vend.c: In function ‘print_re_vend_errlog_scn’:
librtasevent_src/rtas_vend.c:152:55: warning: unused parameter ‘verbosity’ [-Wunused-parameter]
  152 | print_re_vend_errlog_scn(struct scn_header *shdr, int verbosity)
      |                                                   ~~~~^~~~~~~~~

Doesn't seem like too much to fix.