Allow later -z name=<int> args to override earlier args

[rprichard]

Summary

lld already gives later -z options precedence in getZFlag().

This matches the behavior of ld.bfd and ld.gold, where later options
override earlier ones. (I tested with -z max-page-size and -z stack-size.)

[rprichard]

I noticed this issue while experimenting with a new -z option, not when using -z max-page-size or -z stack-size.

[grimar]

LGTM

[ruiu]

LGTM

Common/Args.cpp

std::vector<StringRef> lld::args::getStrings(opt::InputArgList &Args, int Id) {
   std::vector<StringRef> V;
   for (auto *Arg : Args.filtered(Id))
     V.push_back(Arg->getValue());
   return V;
 }
 
 uint64_t lld::args::getZOptionValue(opt::InputArgList &Args, int Id,
                                     StringRef Key, uint64_t Default) {
-  for (auto *Arg : Args.filtered(Id)) {
+  for (auto *Arg : Args.filtered_reverse(Id)) {
     std::pair<StringRef, StringRef> KV = StringRef(Arg->getValue()).split('=');
     if (KV.first == Key) {
       uint64_t Result = Default;
       if (!to_integer(KV.second, Result))
         error("invalid " + Key + ": " + KV.second);
       return Result;
     }
   }

test/ELF/zstack-size.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld -z stack-size=0x1000 %t -o %t1
 # RUN: llvm-readobj -program-headers %t1 | FileCheck %s -check-prefix=CHECK1
 
 # RUN: ld.lld -z stack-size=0 %t -o %t2
 # RUN: llvm-readobj -program-headers %t2 | FileCheck %s -check-prefix=CHECK2
 
+# RUN: ld.lld -z stack-size=0x2000 -z stack-size=0x1000 %t -o %t3
+# RUN: llvm-readobj -program-headers %t3 | FileCheck %s -check-prefix=CHECK1
+
 .global _start
 _start:
   nop
 
 # CHECK1:     Type: PT_GNU_STACK (0x6474E551)
 # CHECK1-NEXT:     Offset: 0x0
 # CHECK1-NEXT:     VirtualAddress: 0x0
 # CHECK1-NEXT:     PhysicalAddress: 0x0