Add test coverage for #error and #warning

This replaces and extends the coverage lost by the removal of
errors testcase pp_deprecated.

See #2635

Examples/test-suite/errors/pp_error_directive.i

@@ -0,0 +1,9 @@
+%module xxx
+
+#warning Print this warning
+
+#error This is an error
+
+#error Another error
+
+#warning Another warning

Examples/test-suite/errors/pp_error_directive.stderr

@@ -0,0 +1,4 @@
+pp_error_directive.i:3: Warning 204: CPP #warning, "Print this warning".
+pp_error_directive.i:5: Error: CPP #error "This is an error". Use the -cpperraswarn option to continue swig processing.
+pp_error_directive.i:7: Error: CPP #error "Another error". Use the -cpperraswarn option to continue swig processing.
+pp_error_directive.i:9: Warning 204: CPP #warning, "Another warning".

Examples/test-suite/preproc_defined.i

@@ -124,6 +124,33 @@ void another_macro_checking(void) {
 # wobble wobble
 #endif
 
+/* Check that #error is ignored inside an inactive conditional. */
+#ifdef THIS_IS_NOT_DEFINED
+# error should not trigger 1
+#endif
+#ifdef AAA
+# define B
+#else
+# error should not trigger 2
+#endif
+#if 0
+# error should not trigger 3
+#endif
+
+/* Check that #warning is ignored inside an inactive conditional. */
+#ifdef THIS_IS_NOT_DEFINED
+# warning should not trigger 1
+#endif
+#ifdef AAA
+# define B
+#else
+# warning should not trigger 2
+#endif
+#if 0
+# warning should not trigger 3
+#endif
+
+
 /* Regression test for https://sourceforge.net/p/swig/bugs/1163/
  * ONE(1)(2) should expand to `2` but SWIG was expanding it to `TWO(2)`
  * which results in the generated C wrapper failing to compile.