Handle -undefined as a synonym for --undefined instead of `-u nde…

…fined`

Fixes #1059

elf/cmdline.cc

@@ -662,7 +662,7 @@ std::vector<std::string> parse_nonpositional_args(Context<E> &ctx) {
         ctx.arg.unresolved_symbols = UNRESOLVED_IGNORE;
       else
         Fatal(ctx) << "unknown --unresolved-symbols argument: " << arg;
-    } else if (read_arg("u") || read_arg("undefined")) {
+    } else if (read_arg("undefined") || read_arg("u")) {
       ctx.arg.undefined.push_back(arg);
     } else if (read_arg("require-defined")) {
       ctx.arg.require_defined.push_back(arg);

test/elf/undefined2.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+test_cflags -static || skip
+
+cat <<EOF | $CC -o $t/a.o -c -x assembler -
+.globl _start
+_start:
+EOF
+
+cat <<EOF | $CC -o $t/b.o -c -x assembler -
+.globl ndefined
+ndefined:
+EOF
+
+cat <<EOF | $CC -o $t/c.o -c -x assembler -
+.globl foo
+foo:
+EOF
+
+rm -f $t/d.a
+ar cr $t/d.a $t/b.o $t/c.o
+
+./mold -static -o $t/exe $t/a.o $t/d.a -undefined foo
+readelf --symbols $t/exe > $t/log
+grep -q foo $t/log
+! grep -q ndefined $t/log || false