pseudotalloc: turn talloc_steal() into #define

Any non-anciant version of talloc implements talloc_steal()
as a #define using the _talloc_steal_loc() symbol.  Let's be
more compatible.

This fix is relevant to using osmo_fsm inside the osmo-ccid-firmware
builds for Cortex-M4.  In this situation, for some strange reason,
libosmcoore is compiled using src/pseudotalloc/talloc.h, but later then
linked against the real libtalloc.

Change-Id: I1ee7f5e9b1002cff37bb8341ad870e1da5f1f9ff
diff --git a/src/pseudotalloc/pseudotalloc.c b/src/pseudotalloc/pseudotalloc.c
index 89e6269..c368296 100644
--- a/src/pseudotalloc/pseudotalloc.c
+++ b/src/pseudotalloc/pseudotalloc.c
@@ -97,7 +97,7 @@
 	return buf;
 }
 
-void *talloc_steal(const void *new_ctx, const void *obj)
+void *_talloc_steal_loc(const void *new_ctx, const void *obj, const char *location)
 {
 	/* as we don't do hierarchical allocations, this is simply a NOP */
 	return (void *)obj;