Modify test to look for patterns in stderr as well

[sepavloff]

Summary

With the change https://reviews.llvm.org/D33013 driver does not build
compilation object if command line is invalid, in particular, if
unrecognized option is provided. In such cases it prints diagnostics
on stderr. The test 'clang-tidy/diagnostic.cpp' checks reaction on
unrecognized option and will fail when D33013 is applied. With this
change the test works in either case.

[alexfh]

Feel free to commit this to fix buildbots, however the underlying D33013 raises some questions.

Clang-tidy is also used as a library, in which case it should capture all compiler diagnostics and pass them to the caller. This test verifies that clang-tidy actually captures the compilation error, and with D33013 this seems to have broken for the diagnostics related to command line parsing. Modifying the driver to directly output these errors to stderr instead of using DiagnosticConsumer seems like a wrong thing to do.

clang-tools-extra/trunk/test/clang-tidy/diagnostic.cpp

 // RUN: clang-tidy -checks='-*,modernize-use-override' %s.nonexistent.cpp -- | FileCheck -check-prefix=CHECK1 -implicit-check-not='{{warning:|error:}}' %s
-// RUN: clang-tidy -checks='-*,clang-diagnostic-*,google-explicit-constructor' %s -- -fan-unknown-option | FileCheck -check-prefix=CHECK2 -implicit-check-not='{{warning:|error:}}' %s
-// RUN: clang-tidy -checks='-*,google-explicit-constructor,clang-diagnostic-literal-conversion' %s -- -fan-unknown-option | FileCheck -check-prefix=CHECK3 -implicit-check-not='{{warning:|error:}}' %s
+// RUN: clang-tidy -checks='-*,clang-diagnostic-*,google-explicit-constructor' %s -- -fan-unknown-option 2>&1 | FileCheck -check-prefix=CHECK2 -implicit-check-not='{{warning:|error:}}' %s
+// RUN: clang-tidy -checks='-*,google-explicit-constructor,clang-diagnostic-literal-conversion' %s -- -fan-unknown-option 2>&1 | FileCheck -check-prefix=CHECK3 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: clang-tidy -checks='-*,modernize-use-override,clang-diagnostic-macro-redefined' %s -- -DMACRO_FROM_COMMAND_LINE | FileCheck -check-prefix=CHECK4 -implicit-check-not='{{warning:|error:}}' %s
 
 // CHECK1: error: error reading '{{.*}}.nonexistent.cpp' [clang-diagnostic-error]
-// CHECK2: error: unknown argument: '-fan-unknown-option' [clang-diagnostic-error]
-// CHECK3: error: unknown argument: '-fan-unknown-option' [clang-diagnostic-error]
+// CHECK2: error: unknown argument: '-fan-unknown-option'
+// CHECK3: error: unknown argument: '-fan-unknown-option'
 
 // CHECK2: :[[@LINE+2]]:9: warning: implicit conversion from 'double' to 'int' changes value from 1.5 to 1 [clang-diagnostic-literal-conversion]
 // CHECK3: :[[@LINE+1]]:9: warning: implicit conversion from 'double' to 'int' changes value
 int a = 1.5;
 
 // CHECK2: :[[@LINE+2]]:11: warning: single-argument constructors must be marked explicit
 // CHECK3: :[[@LINE+1]]:11: warning: single-argument constructors must be marked explicit
 class A { A(int) {} };
 
 #define MACRO_FROM_COMMAND_LINE
 // CHECK4: :[[@LINE-1]]:9: warning: 'MACRO_FROM_COMMAND_LINE' macro redefined