libs/pipewire: guard Linux-only MAP_LOCKED + prctl for Redox

Port pipewire's Linux-isms to Redox (baked into vendored source/):
 - mem.c: add __redox__ to the BSD/GNU guard that #defines MAP_LOCKED 0 (Redox
   has no page-locking; the flag is a no-op).
 - pipewire.c: guard #include <sys/prctl.h> and the prctl(PR_GET_NAME) thread-
   name block for __redox__ (Redox has no prctl; thread naming is skipped).
alloca resolved on a clean cook (-include alloca.h + staged relibc alloca.h).

local/recipes/libs/pipewire/source/src/pipewire/mem.c

@@ -68,7 +68,7 @@ static inline int memfd_create(const char *name, unsigned int flags)
 #define HAVE_MEMFD_CREATE 1
 #endif
 
-#if defined(__FreeBSD__) || defined(__MidnightBSD__) || defined(__GNU__)
+#if defined(__FreeBSD__) || defined(__MidnightBSD__) || defined(__GNU__) || defined(__redox__)
 #define MAP_LOCKED 0
 #endif
 

local/recipes/libs/pipewire/source/src/pipewire/pipewire.c

@@ -8,8 +8,10 @@
 #include <limits.h>
 #include <stdio.h>
 #if !defined(__FreeBSD__) && !defined(__MidnightBSD__) && !defined(__GNU__)
+#ifndef __redox__
 #include <sys/prctl.h>
 #endif
+#endif
 #include <pwd.h>
 #include <errno.h>
 #include <dlfcn.h>
@@ -738,7 +740,7 @@ static void init_prgname(void)
 		}
 	}
 #endif
-#if !defined(__FreeBSD__) && !defined(__MidnightBSD__) && !defined(__GNU__)
+#if !defined(__FreeBSD__) && !defined(__MidnightBSD__) && !defined(__GNU__) && !defined(__redox__)
 	{
 		if (prctl(PR_GET_NAME, (unsigned long) name, 0, 0, 0) == 0) {
 			prgname = name;