[ELF] Change duplicate symbol errors to use errorOrWarn

so that --noinhibit-exec downgrades the error to a warning, which
matches GNU ld. Most recoverable errors should use errorOrWarn.

Author: MaskRay

lld/ELF/Symbols.cpp

@@ -539,8 +539,8 @@ void elf::reportDuplicate(const Symbol &sym, const InputFile *newFile,
   if (!d->section && !errSec && errOffset && d->value == errOffset)
     return;
   if (!d->section || !errSec) {
-    error("duplicate symbol: " + toString(sym) + "\n>>> defined in " +
-          toString(sym.file) + "\n>>> defined in " + toString(newFile));
+    errorOrWarn("duplicate symbol: " + toString(sym) + "\n>>> defined in " +
+                toString(sym.file) + "\n>>> defined in " + toString(newFile));
     return;
   }
 
@@ -564,7 +564,7 @@ void elf::reportDuplicate(const Symbol &sym, const InputFile *newFile,
   if (!src2.empty())
     msg += src2 + "\n>>>            ";
   msg += obj2;
-  error(msg);
+  errorOrWarn(msg);
 }
 
 void Symbol::checkDuplicate(const Defined &other) const {

lld/test/ELF/allow-multiple-definition.s

@@ -9,6 +9,9 @@
 # RUN: llvm-objdump --no-print-imm-hex -d %t3 | FileCheck %s
 # RUN: llvm-objdump --no-print-imm-hex -d %t4 | FileCheck --check-prefix=REVERT %s
 
+# RUN: ld.lld --noinhibit-exec %t2 %t1 -o /dev/null 2>&1 | FileCheck %s --check-prefix=WARN
+# WARN: warning: duplicate symbol: _bar
+
 # RUN: ld.lld -z muldefs --fatal-warnings  %t1 %t2 -o %t3
 # RUN: ld.lld -z muldefs --fatal-warnings  %t2 %t1 -o %t4
 # RUN: llvm-objdump --no-print-imm-hex -d %t3 | FileCheck %s