[llvm] [z/OS] Add z/OS archive reading support (PR #187110)

[zhijian lin via llvm-commits]

================
@@ -1171,6 +1307,9 @@ Archive::symbol_iterator Archive::symbol_begin() const {
     buf += ran_strx;
   } else if (kind() == K_AIXBIG) {
     buf = getStringTable().begin();
+  } else if (kind() == K_ZOS) {
+    uint32_t symbol_count = read32be(buf);
+    buf += sizeof(uint32_t) + (symbol_count * (sizeof(uint64_t)));
----------------
diggerlin wrote:

please add some comment for the code 
`buf += sizeof(uint32_t) + (symbol_count * (sizeof(uint64_t)));`

I think you reorganize your above comment to explain above code. 
    // The contents of the symbol table member in order are:
    // 1. The number of symbols, NS (4 byte integer).
    // 2. NS pairs of integers (the first in each pair of integers is the offset
    //    to the header of the entry... the second being coded attributes).
    //    Length is NS*(4+4) bytes.
    // 3. NS null terminated strings of corresponding symbol names.

https://github.com/llvm/llvm-project/pull/187110