[PATCH] gdbsupport: fix array-view compilation with c++11 && _GLIBCXX_DEBUG

[Simon Marchi <simon.marchi@efficios.com>]

When building with -std=c++11 and -D_GLIBCXX_DEBUG=1, we get some errors
like:

      CXX    unittests/array-view-selftests.o
    In file included from /home/smarchi/src/binutils-gdb/gdb/utils.h:25,
                     from /home/smarchi/src/binutils-gdb/gdb/defs.h:630,
                     from /home/smarchi/src/binutils-gdb/gdb/unittests/array-view-selftests.c:20:
    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/array-view.h: In instantiation of ‘constexpr gdb::array_view<T> gdb::array_view<T>::slice(gdb::array_view<T>::size_type, gdb::array_view<T>::size_type) const [with T = unsigned char; gdb::array_view<T>::size_type = long unsigned int]’:
    /home/smarchi/src/binutils-gdb/gdb/unittests/array-view-selftests.c:532:29:   required from here
    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/array-view.h:192:3: error: body of ‘constexpr’ function ‘constexpr gdb::array_view<T> gdb::array_view<T>::slice(gdb::array_view<T>::size_type, gdb::array_view<T>::size_type) const [with T = unsigned char; gdb::array_view<T>::size_type = long unsigned int]’ not a return-statement
      192 |   }
          |   ^

This is because constexpr functions in C++ can only consist of a single
return statement, so we can't have the gdb_assert in there.  Make the
gdb_assert presence conditional to the __cplusplus version, to enable it
only for c++14 and later.

Change-Id: I2ac33f7b4bd1765ddc3ac8d07445b16ac1f340f0
---
 gdbsupport/array-view.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/gdbsupport/array-view.h b/gdbsupport/array-view.h
index 6f7e45a979c..edf66559e2d 100644
--- a/gdbsupport/array-view.h
+++ b/gdbsupport/array-view.h
@@ -171,7 +171,7 @@ class array_view
   }
   constexpr const_reference operator[] (size_t index) const noexcept
   {
-#if defined(_GLIBCXX_DEBUG)
+#if defined(_GLIBCXX_DEBUG) && __cplusplus >= 201402L
     gdb_assert (index < m_size);
 #endif
     return m_array[index];
@@ -185,7 +185,7 @@ class array_view
   /* Return a new array view over SIZE elements starting at START.  */
   constexpr array_view<T> slice (size_type start, size_type size) const noexcept
   {
-#if defined(_GLIBCXX_DEBUG)
+#if defined(_GLIBCXX_DEBUG) && __cplusplus >= 201402L
     gdb_assert (start + size <= m_size);
 #endif
     return {m_array + start, size};
@@ -195,7 +195,7 @@ class array_view
      inclusive.  */
   constexpr array_view<T> slice (size_type start) const noexcept
   {
-#if defined(_GLIBCXX_DEBUG)
+#if defined(_GLIBCXX_DEBUG) && __cplusplus >= 201402L
     gdb_assert (start <= m_size);
 #endif
     return {m_array + start, size () - start};
-- 
2.33.1