testsuite: c++: Allow for std::printf in g++.dg/modules/stdio-1_a.H [PR98529]

g++.dg/modules/stdio-1_a.H currently FAILs on Solaris:

FAIL: g++.dg/modules/stdio-1_a.H -std=c++17  scan-lang-dump module "Depset:0 decl entity:[0-9]* function_decl:'::printf'"
FAIL: g++.dg/modules/stdio-1_a.H -std=c++2a  scan-lang-dump module "Depset:0 decl entity:[0-9]* function_decl:'::printf'"
FAIL: g++.dg/modules/stdio-1_a.H -std=c++2b  scan-lang-dump module "Depset:0 decl entity:[0-9]* function_decl:'::printf'"

The problem is that the module file doesn't contain

 Depset:0 decl entity:95 function_decl:'::printf'

as expected by the test, but

 Depset:0 decl entity:26 function_decl:'::std::printf'

This happens because Solaris <stdio.h> declares printf in namespace std
as allowed by C++11, Annex D, D.5.

This patch allows for both forms.

Tested on i386-pc-solaris2.11, sparc-sun-solaris2.11, and
x86_64-pc-linux-gnu.

2024-05-13  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	PR c++/98529
	* g++.dg/modules/stdio-1_a.H (scan-lang-dump): Allow for
	::std::printf.