Gallium: Use mmap on Haiku for executable memory vs malloc

* Haiku now has DEP enabled by default.

src/gallium/auxiliary/rtasm/rtasm_execmem.c

@@ -49,7 +49,7 @@
 #include <windows.h>
 #endif
 
-#if defined(PIPE_OS_LINUX) || defined(PIPE_OS_BSD) || defined(PIPE_OS_SOLARIS)
+#if defined(PIPE_OS_LINUX) || defined(PIPE_OS_BSD) || defined(PIPE_OS_SOLARIS) || defined(PIPE_OS_HAIKU)
 
 
 /*