add a test to verify that compile-flags are provided last

Author: pietroalbini

src/test/ui/compiletest-compile-flags-last.rs

@@ -0,0 +1,6 @@
+// Check that the arguments provided through `// compile-flags` are added last to the command line
+// in UI tests. To ensure that we invoke rustc with a flag that expects an argument withut actually
+// providing it. If the compile-flags are not last, the test will fail as rustc will interpret the
+// next flag as the argument of this flag.
+//
+// compile-flags: --cap-lints

src/test/ui/compiletest-compile-flags-last.stderr

@@ -0,0 +1,2 @@
+error: Argument to option 'cap-lints' missing
+

src/tools/tidy/src/ui_tests.rs

@@ -7,7 +7,7 @@ use std::path::Path;
 
 const ENTRY_LIMIT: usize = 1000;
 // FIXME: The following limits should be reduced eventually.
-const ROOT_ENTRY_LIMIT: usize = 948;
+const ROOT_ENTRY_LIMIT: usize = 949;
 const ISSUES_ENTRY_LIMIT: usize = 2117;
 
 fn check_entries(path: &Path, bad: &mut bool) {