Prevent erroneous "macro had not yet been defined" messages (PR c++/85385)

Prevent erroneous "macro had not yet been defined" messages (PR c++/85385)

PR c++/85385 reports an issue where we emit bogus "macro had not yet been
defined" notes when a macro is mis-used:

  $ cat test.c
  #define MACRO(X,Y)

  void test ()
  {
    MACRO(42);
  }

  $ ./xg++ -B. -c test.c
  test.c:5:11: error: macro "MACRO" requires 2 arguments, but only 1 given
     MACRO(42);
             ^
  test.c: In function ‘void test()’:
  test.c:5:3: error: ‘MACRO’ was not declared in this scope
     MACRO(42);
     ^~~~~
  test.c:5:3: note:
  test.c:1: note: it was later defined here
   #define MACRO(X,Y)

The macro *had* been defined, it was merely misused.

This patch fixes the issue by only issuing the note if the use location
is before the definition location (using linemap_location_before_p).

gcc/cp/ChangeLog:
	PR c++/85385
	* name-lookup.c (macro_use_before_def::maybe_make): New function,
	checking that the use is indeed before the definition.
	(macro_use_before_def::macro_use_before_def): Make private.
	(macro_use_before_def::~macro_use_before_def): Make private.  Move
	check for UNKNOWN_LOCATION to macro_use_before_def::maybe_make.
	(lookup_name_fuzzy): Call macro_use_before_def::maybe_make rather
	than using new directly.

gcc/testsuite/ChangeLog:
	PR c++/85385
	* g++.dg/diagnostic/macro-arg-count.C: New test.

From-SVN: r259360