[dsymutil] Generalize handling of aliases external symbols

In f9fb9da36c we fixed spurious warnings
caused by aliases to private extern symbols. This patch generalizes that
to regular external symbols as well.

llvm/test/tools/dsymutil/ARM/extern-alias.test

@@ -10,6 +10,18 @@ int* bar() {
   return foo();
 }
 
+$ cat extern.c
+__attribute__((visibility("hidden")))
+int* foo() {
+  int i = 10;
+  volatile int* j = &i;
+  return j;
+}
+
+int* bar() {
+  return foo();
+}
+
 $ cat main.c
 int* bar();
 int main() {
@@ -24,6 +36,7 @@ $ xcrun --sdk iphoneos clang -g main.c -c -o main.o -target arm64-apple-ios14.0
 $ xcrun --sdk iphoneos clang private_extern.o main.o -target arm64-apple-ios14.0 -o private_extern.out -Xlinker -alias_list -Xlinker alias_list
 
 RUN: dsymutil -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/private_extern/private_extern.out -o %t.dSYM --verbose 2>&1 | FileCheck %s
+RUN: dsymutil -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/extern/extern.out -o %t.dSYM --verbose 2>&1 | FileCheck %s
 CHECK-NOT: could not find object file symbol for symbol _baz
 CHECK: { sym: _foo, objAddr: 0x0000000000000000, binAddr: 0x0000000100007F58, size: 0x00000020 }
 CHECK: { sym: _baz, objAddr: 0x0000000000000000, binAddr: 0x0000000100007F58, size: 0x00000000 }

llvm/tools/dsymutil/MachODebugMapParser.cpp

@@ -562,9 +562,7 @@ void MachODebugMapParser::loadMainBinarySymbols(
       continue;
     }
     Section = *SectionOrErr;
-    if ((Section == MainBinary.section_end() || Section->isText()) &&
-        !(SymType &
-          MachO::N_PEXT)) // Alias to non-external (was a private external)
+    if ((Section == MainBinary.section_end() || Section->isText()) && !Extern)
       continue;
     uint64_t Addr = cantFail(Sym.getValue());
     Expected<StringRef> NameOrErr = Sym.getName();