[Sanitizers] Provide __internal_dup on Solaris

[ro]

Summary

Both LLVM 8.0.0 and current trunk fail to link `libclang_rt.ubsan.standalone-*.so```
on Solaris 11/x86 with GCC 8.1.0:

Undefined			first referenced
 symbol  			    in file
Scanning dependencies of target clang_rt.asan_cxx-x86_64
__sanitizer::internal_dup(int)      ../sanitizer_common/CMakeFiles/RTSanitizerCommon.i386.dir/sanitizer_posix.cc.o
ld: fatal: symbol referencing errors
collect2: error: ld returned 1 exit status
make[2]: *** [projects/compiler-rt/lib/ubsan/CMakeFiles/clang_rt.ubsan_standalone-dynamic-i386.dir/build.make:233: lib/clang/9.0.0/lib/sunos/libclang_rt.ubsan_standalone-i386.so] Error 1

Fixed by providing an implementation, which allowed the i386-pc-solaris2.11 build
to finish.

[ro]

Ping. Given that this patch is Solaris-only, I guess it could go in as obvious?

[eugenis]

Yes, seems pretty obvious.
LGTM.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_solaris.cc

 
 uptr internal_filesize(fd_t fd) {
   struct stat st;
   if (internal_fstat(fd, &st))
     return -1;
   return (uptr)st.st_size;
 }
 
+DECLARE__REAL_AND_INTERNAL(uptr, dup, int oldfd) {
+  return _REAL(dup)(oldfd);
+}
+
 DECLARE__REAL_AND_INTERNAL(uptr, dup2, int oldfd, int newfd) {
   return _REAL(dup2)(oldfd, newfd);
 }
 
 DECLARE__REAL_AND_INTERNAL(uptr, readlink, const char *path, char *buf,
                            uptr bufsize) {
   return _REAL(readlink)(path, buf, bufsize);
 }