On MIPS, libsanitizer appears to have very detailed knowledge of the
Linux system call ABI manually encoded, by hand, into the library.
This encoding covers the o32 and 64 abis, but does not cover n32.
Adding support for n32 would be a major undertaking.

Without adding this encoding, builds of gcc will fail with errors
including (but not limited to) the following:

```
In file included from ../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_platform_limits_linux.cpp:21:
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_platform_limits_linux.cpp:75:38: error: static assertion failed
   75 | COMPILER_CHECK(struct_kernel_stat_sz == sizeof(struct stat));
      |                ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_internal_defs.h:348:44: note: in definition of macro 'COMPILER_CHECK'
  348 | #define COMPILER_CHECK(pred) static_assert(pred, "")
      |                                            ^~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_platform_limits_linux.cpp:75:38: note: the comparison reduces to '(144 == 160)'
   75 | COMPILER_CHECK(struct_kernel_stat_sz == sizeof(struct stat));
      |                ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_internal_defs.h:348:44: note: in definition of macro 'COMPILER_CHECK'
  348 | #define COMPILER_CHECK(pred) static_assert(pred, "")
      |                                            ^~~~
...
In file included from ../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:184:
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: In function '__sanitizer::uptr __sanitizer::internal_mmap(void*, uptr, int, int, int, u64)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_syscall_generic.inc:19:24: error: '__NR_mmap2' was not declared in this scope
   19 | # define SYSCALL(name) __NR_ ## name
      |                        ^~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:198:27: note: in expansion of macro 'SYSCALL'
  198 |   return internal_syscall(SYSCALL(mmap2), addr, length, prot, flags, fd,
      |                           ^~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: In function 'void __sanitizer::stat64_to_stat(stat64*, stat*)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:279:23: error: 'struct stat64' has no member named 'st_atim'; did you mean 'st_atime'?
  279 |   out->st_atime = in->st_atime;
      |                       ^~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:280:23: error: 'struct stat64' has no member named 'st_mtim'; did you mean 'st_mtime'?
  280 |   out->st_mtime = in->st_mtime;
      |                       ^~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:281:23: error: 'struct stat64' has no member named 'st_ctim'; did you mean 'st_ctime'?
  281 |   out->st_ctime = in->st_ctime;
      |                       ^~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: In function '__sanitizer::uptr __sanitizer::internal_stat(const char*, void*)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_syscall_generic.inc:19:24: error: '__NR_stat64' was not declared in this scope
   19 | # define SYSCALL(name) __NR_ ## name
      |                        ^~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:353:30: note: in expansion of macro 'SYSCALL'
  353 |   int res = internal_syscall(SYSCALL(stat64), path, &buf64);
      |                              ^~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: In function '__sanitizer::uptr __sanitizer::internal_lstat(const char*, void*)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_syscall_generic.inc:19:24: error: '__NR_lstat64' was not declared in this scope
   19 | # define SYSCALL(name) __NR_ ## name
      |                        ^~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:378:30: note: in expansion of macro 'SYSCALL'
  378 |   int res = internal_syscall(SYSCALL(lstat64), path, &buf64);
      |                              ^~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: In function '__sanitizer::uptr __sanitizer::internal_fstat(fd_t, void*)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_syscall_generic.inc:19:24: error: '__NR_fstat64' was not declared in this scope
   19 | # define SYSCALL(name) __NR_ ## name
      |                        ^~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:397:30: note: in expansion of macro 'SYSCALL'
  397 |   int res = internal_syscall(SYSCALL(fstat64), fd, &buf64);
      |                              ^~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp: At global scope:
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_linux.cpp:303:13: warning: 'void __sanitizer::kernel_stat_to_stat(kernel_stat*, stat*)' defined but not used [8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wunused-function-Wunused-function8;;]
  303 | static void kernel_stat_to_stat(struct kernel_stat *in, struct stat *out) {
      |             ^~~~~~~~~~~~~~~~~~~
mv -f .deps/sanitizer_mutex.Tpo .deps/sanitizer_mutex.Plo
make[4]: *** [Makefile:617: sanitizer_linux.lo] Error 1
mv -f .deps/sancov_flags.Tpo .deps/sancov_flags.Plo
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_posix.cpp: In function '__sanitizer::fd_t __sanitizer::OpenFile(const char*, FileAccessMode, error_t*)':
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_posix.cpp:162:27: warning: 'flags' may be used uninitialized [8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmaybe-uninitialized-Wmaybe-uninitialized8;;]
  162 |   fd_t res = internal_open(filename, flags, 0660);
      |              ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
../../../../gcc-12.2.0/libsanitizer/sanitizer_common/sanitizer_posix.cpp:156:7: note: 'flags' was declared here
  156 |   int flags;
      |       ^~~~~
```