testsuite: Fix C++11 compilation failure for gdb.cp/m-static.exp

gcc-6.2.1-1.fc26.x86_64

g++ -std=c++03:
no warnings

g++:
In file included from /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.cc:79:0:
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.h:9:34: error: ‘constexpr’ needed for in-class initialization of static
data member ‘const float gnu_obj_4::somewhere’ of non-integral type [-fpermissive]
   static const float somewhere = 3.14159;
                                  ^~~~~~~

clang++:
In file included from /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.cc:79:
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.h:9:22: warning: in-class initializer for static data member of type 'const
float' is a GNU extension [-Wgnu-static-float-init]
  static const float somewhere = 3.14159;
                     ^           ~~~~~~~
1 warning generated.

clang++ -std=c++11:
In file included from /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.cc:79:
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.h:9:22: error: in-class initializer for static data member of type 'const
float' requires 'constexpr' specifier [-Wstatic-float-init]
  static const float somewhere = 3.14159;
                     ^           ~~~~~~~
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.h:9:3: note: add 'constexpr'
  static const float somewhere = 3.14159;
  ^
  constexpr
1 error generated.

OK for check-in?

After the fix out of the 4 combinations above only this one remains non-empty:

clang++:
In file included from /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.cc:79:
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/m-static.h:9:22: warning: in-class initializer for static data member of type 'const
float' is a GNU extension [-Wgnu-static-float-init]
  static const float somewhere = 3.14159;
                     ^           ~~~~~~~
1 warning generated.

On Thu, 15 Sep 2016 15:10:50 +0200, Pedro Alves wrote:

Hmm, OK, now that I read the test, I think you were right in trying to
keep it safe, actually.  The .exp file has:

if { $non_dwarf } { setup_xfail *-*-* }
gdb_test "print test4.everywhere" "\\$\[0-9\].* = 317" "static const int initialized in class definition"
if { $non_dwarf } { setup_xfail *-*-* }
gdb_test "print test4.somewhere" "\\$\[0-9\].* = 3.14\[0-9\]*" "static const float initialized in class definition"
                                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Added by this:

 https://sourceware.org/bugzilla/show_bug.cgi?id=11702
 https://sourceware.org/ml/gdb-patches/2010-06/msg00677.html
 https://sourceware.org/ml/gdb-patches/2010-06/txt00011.txt

So the new patch would make that highlighted tested above not
test what its test message says it is testing.

So I now think your original patch is better.  Please push
that one instead.

gdb/testsuite/ChangeLog
2016-09-15  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.cp/m-static.h (gnu_obj_4::somewhere): Use constexpr for C++11.

2 files changed, 7 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8e02eeb5ff2..15db4ea9403 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-09-15  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* gdb.cp/m-static.h (gnu_obj_4::somewhere): Use constexpr for C++11.
+
 2016-09-15  Peter Bergner  <bergner@vnet.ibm.com>
 
 	* gdb.arch/powerpc-power.s: Update Power9 instruction tests
diff --git a/gdb/testsuite/gdb.cp/m-static.h b/gdb/testsuite/gdb.cp/m-static.h
index bcedfff4eea..29924638112 100644
--- a/gdb/testsuite/gdb.cp/m-static.h
+++ b/gdb/testsuite/gdb.cp/m-static.h
@@ -6,6 +6,9 @@ class gnu_obj_4
   static const int elsewhere;
   static const int nowhere;
   static const int everywhere = 317;
+#if __cplusplus >= 201103L
+  constexpr
+#endif
   static const float somewhere = 3.14159;
 
   // try to ensure test4 is actually allocated