[gcc r12-7938] libstdc++: Add comment about memalign requirements

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:7f016919fc8a042b83812ae5f34946ef23b7adb3

commit r12-7938-g7f016919fc8a042b83812ae5f34946ef23b7adb3
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 30 16:57:27 2022 +0100

    libstdc++: Add comment about memalign requirements
    
    The memalign man page on Solaris and QNX lists an additional requirement
    for the alignment value that is not present in all implementation of
    that non-standard function. For both those targets we should actually be
    using posix_memalign anyway, so it doesn't matter. This just adds a
    comment making note of that fact.
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/new_opa.cc (aligned_alloc): Add comment.

Diff:
---
 libstdc++-v3/libsupc++/new_opa.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 5f24737de1c..411cd8d98b2 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -87,6 +87,8 @@ aligned_alloc (std::size_t al, std::size_t sz)
 static inline void*
 aligned_alloc (std::size_t al, std::size_t sz)
 {
+  // Solaris requires al >= sizeof a word and QNX requires >= sizeof(void*)
+  // but they both provide posix_memalign, so will use the definition above.
   return memalign (al, sz);
 }
 #else // !HAVE__ALIGNED_MALLOC && !HAVE_POSIX_MEMALIGN && !HAVE_MEMALIGN