fix Args function broken in r281942

The method was hard-coded to check only the 0th element of the array.
This manifested as NSLog messages behaving incorrectly on macOS.
(This is independent of the broken DarwinLog feature).

llvm-svn: 282128
diff --git a/lldb/source/Interpreter/Args.cpp b/lldb/source/Interpreter/Args.cpp
index 6b6fe46..36ea78c 100644
--- a/lldb/source/Interpreter/Args.cpp
+++ b/lldb/source/Interpreter/Args.cpp
@@ -1002,7 +1002,7 @@
 
   // Check each arg to see if it matches the env var name.
   for (size_t i = 0; i < GetArgumentCount(); ++i) {
-    auto arg_value = llvm::StringRef::withNullAsEmpty(GetArgumentAtIndex(0));
+    auto arg_value = llvm::StringRef::withNullAsEmpty(GetArgumentAtIndex(i));
 
     llvm::StringRef name, value;
     std::tie(name, value) = arg_value.split('=');