libphobos: Merge upstream phobos 791c5d240

Adds missing HPPA support in std.experimental.allocator.

Reviewed-on: https://github.com/dlang/phobos/pull/6838

From-SVN: r268810

libphobos/src/MERGE

-6c9fb28b0f8813d41798202a9d19c6b37ba5da5f
+791c5d2407e500bb4e777d6a90fc96cf250ba2f6
 
 The first line of this file holds the git revision number of the last
 merge done from the dlang/phobos repository.

libphobos/src/std/experimental/allocator/building_blocks/region.d

@@ -387,6 +387,7 @@ struct InSituRegion(size_t size, size_t minAlign = platformAlignment)
     else version (X86_64) enum growDownwards = Yes.growDownwards;
     else version (ARM) enum growDownwards = Yes.growDownwards;
     else version (AArch64) enum growDownwards = Yes.growDownwards;
+    else version (HPPA) enum growDownwards = No.growDownwards;
     else version (PPC) enum growDownwards = Yes.growDownwards;
     else version (PPC64) enum growDownwards = Yes.growDownwards;
     else version (MIPS32) enum growDownwards = Yes.growDownwards;