This changes from:

pragma-diag-3.c:2:9: warning: missing [error|warning|ignored] after
‘#pragma GCC diagnostic’ [-Wpragmas]
 #pragma GCC diagnostic /* { dg-warning "24:missing" "missing" { xfail
*-*-* } } */
         ^
pragma-diag-3.c:4:9: warning: expected
[error|warning|ignored|push|pop] after ‘#pragma GCC diagnostic’
[-Wpragmas]
 #pragma GCC diagnostic warn /* { dg-warning "24:expected" } */
         ^
pragma-diag-3.c:6:9: warning: unknown option after ‘#pragma GCC
diagnostic’ kind [-Wpragmas]
 #pragma GCC diagnostic ignored "-Wfoo" /* { dg-warning "32:unknown" } */
         ^

to:


pragma-diag-3.c:2:83: warning: missing
[error|warning|ignored|push|pop] after ‘#pragma GCC diagnostic’
[-Wpragmas]
pragma-diag-3.c:4:24: warning: expected
[error|warning|ignored|push|pop] after ‘#pragma GCC diagnostic’
[-Wpragmas]
 #pragma GCC diagnostic warn /* { dg-warning "24:expected" } */
                        ^
pragma-diag-3.c:6:32: warning: unknown option after ‘#pragma GCC
diagnostic’ kind [-Wpragmas]
 #pragma GCC diagnostic ignored "-Wfoo" /* { dg-warning "32:unknown" } */
                                ^

which is a clear improvement except for the fact that CPP_PRAGMA_EOL
tokens do not have a valid location. I think this is a bug and will
open a PR.

Of course, this opens the door to giving better locations for all
diagnostics in c-pragma.c, but I'll leave that for the future.

Bootstrapped and regression tested on x86_64-linux-gnu.

OK?

gcc/cp/ChangeLog:

2015-05-25  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * parser.c (pragma_lex): Add loc argument. Rearrange the code to
    make it more similar to the C version.

gcc/c-family/ChangeLog:

2015-05-25  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * c-pragma.c (handle_pragma_diagnostic): Use explicit location
    when warning.
    * c-pragma.h (pragma_lex): Add optional loc argument.

gcc/c/ChangeLog:

2015-05-25  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * c-parser.c (pragma_lex): Add loc argument.

gcc/testsuite/ChangeLog:

2015-05-25  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    * gcc.dg/pragma-diag-3.c: New test.