x86-vxworks malloc aligns to 8 bytes like solaris

Vxworks 7's malloc, like Solaris', only ensures 8-byte alignment of
returned pointers on 32-bit x86, though GCC's stddef.h defines
max_align_t with 16-byte alignment for __float128.  This patch enables
on x86-vxworks the same memory_resource workaround used for x86-solaris.

The testsuite also had a workaround, defining BAD_MAX_ALIGN_T and
xfailing the test; extend those to x86-vxworks as well, and remove the
check for char-aligned requested allocation to be aligned like
max_align_t.  With that change, the test passes on x86-vxworks; I'm
guessing that's the same reason for the test not to pass on
x86-solaris (and on x86_64-solaris -m32), so with the fix, I'm
tentatively removing the xfail.


for libstdc++-v3/ChangeLog

	PR libstdc++/77691
	* include/experimental/memory_resource
	(__resource_adaptor_imp::do_allocate): Handle max_align_t on
	x86-vxworks as on x86-solaris.
	(__resource_adaptor_imp::do_deallocate): Likewise.
	* testsuite/experimental/memory_resource/new_delete_resource.cc:
	Drop xfail.
	(BAD_MAX_ALIGN_T): Define on x86-vxworks as on x86-solaris.
	(test03): Drop max-align test for char-aligned alloc.

(cherry picked from commit 883246530f1bb10d854f455e1c3d55b93675690a)

libstdc++-v3/include/experimental/memory_resource

@@ -413,7 +413,7 @@ namespace pmr {
       do_allocate(size_t __bytes, size_t __alignment) override
       {
 	// Cannot use max_align_t on 32-bit Solaris x86, see PR libstdc++/77691
-#if ! (defined __sun__ && defined __i386__)
+#if ! ((defined __sun__ || defined __VXWORKS__) && defined __i386__)
 	if (__alignment == alignof(max_align_t))
 	  return _M_allocate<alignof(max_align_t)>(__bytes);
 #endif
@@ -439,7 +439,7 @@ namespace pmr {
       do_deallocate(void* __ptr, size_t __bytes, size_t __alignment) noexcept
       override
       {
-#if ! (defined __sun__ && defined __i386__)
+#if ! ((defined __sun__ || defined __VXWORKS__) && defined __i386__)
 	if (__alignment == alignof(max_align_t))
 	  return (void) _M_deallocate<alignof(max_align_t)>(__ptr, __bytes);
 #endif

libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc

@@ -17,13 +17,12 @@
 
 // { dg-do run { target c++14 } }
 // { dg-require-cstdint "" }
-// { dg-xfail-run-if "PR libstdc++/77691" { { i?86-*-solaris2.* x86_64-*-solaris2.* } && ilp32 } }
 
 #include <experimental/memory_resource>
 #include <cstdlib>
 #include <testsuite_hooks.h>
 
-#if defined __sun__ && defined __i386__
+#if (defined __sun__ || defined __VXWORKS__) && defined __i386__
 // See PR libstdc++/77691
 # define BAD_MAX_ALIGN_T 1
 #endif
@@ -128,7 +127,6 @@ test03()
 
   p = r1->allocate(2, alignof(char));
   VERIFY( bytes_allocated == 2 );
-  VERIFY( aligned<max_align_t>(p) );
   r1->deallocate(p, 2, alignof(char));
   VERIFY( bytes_allocated == 0 );