binutils/testsuite: skip gentestdlls related tests if missing

When launching the testsuite through runtest outside the build tree,
gentestdlls might not be available, this binary being created by make
check.
Simply untested the related tests instead of crashing.

binutils/ChangeLog:

	* testsuite/binutils-all/objdump.exp: Skip dotnet tests if
	gentestdlls is not available.

binutils/testsuite/binutils-all/objdump.exp

@@ -787,6 +787,12 @@ proc test_objdump_dotnet_assemblies {} {
 
     set test "dotnet-assemblies"
 
+    # If gentestdlls isn't available, skip instead of crashing below.
+    if ![file exists $base_dir/testsuite/gentestdlls] {
+	untested $test
+	return
+    }
+
     set got [binutils_run "$base_dir/testsuite/gentestdlls" "tmpdir pei-i386 pei-x86-64"]
     set want "wrote linux-pei-x86-64.dll"
     # The test program is hardcoded to generate valid dlls on any target