In this third instalment the diagnostic machinery -- when faced with
the virtual location of a token resulting from macro expansion -- uses
the new linemap APIs to unwind the stack of macro expansions that led
to that token and emits a [hopefully] more useful message than what we
have today.

diagnostic_report_current_module has been slightly changed to use the
location given by client code instead of the global input_location
variable.  This results in more precise diagnostic locations in
general but then the patch adjusts some C++ tests which output changed
as a result of this.

Three new regression tests have been added.

The mandatory screenshot goes like this:

[dodji@adjoa gcc]$ cat -n test.c
     1    #define OPERATE(OPRD1, OPRT, OPRD2) \
     2      OPRD1 OPRT OPRD2;
     3
     4    #define SHIFTL(A,B) \
     5      OPERATE (A,<<,B)
     6
     7    #define MULT(A) \
     8      SHIFTL (A,1)
     9
    10    void
    11    g ()
    12    {
    13      MULT (1.0);/* 1.0 << 1; <-- so this is an error.  */
    14    }

[dodji@adjoa gcc]$ ./cc1 -quiet -ftrack-macro-expansion test.c
test.c: In function 'g':
test.c:5:14: erreur: invalid operands to binary << (have 'double' and 'int')
test.c:2:9: note: in expansion of macro 'OPERATE'
test.c:5:3: note: expanded from here
test.c:5:14: note: in expansion of macro 'SHIFTL'
test.c:8:3: note: expanded from here
test.c:8:3: note: in expansion of macro 'MULT2'
test.c:13:3: note: expanded from here

Co-Authored-By: Dodji Seketeli <dodji@redhat.com>

From-SVN: r180083