[MIPS] Enable descriptors for nested functions in Ada

[Eric Botcazou]

Similarly to x86, PowerPC and SPARC, this enables the use of custom run-time 
descriptors in Ada, thus eliminating the need for trampolines and executable 
stack in presence of pointers to nested functions.

Unfortunately I don't have access to MIPS hardware any more, but the scheme 
was tested on the architecture at some point.  OK for the mainline?


2016-11-13  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/67205
        * config/mips/mips.c (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Define.

-- 
Eric Botcazou
Index: config/mips/mips.c
===================================================================
--- config/mips/mips.c	(revision 242334)
+++ config/mips/mips.c	(working copy)
@@ -22387,6 +22387,10 @@ mips_promote_function_mode (const_tree t
 #undef TARGET_HARD_REGNO_SCRATCH_OK
 #define TARGET_HARD_REGNO_SCRATCH_OK mips_hard_regno_scratch_ok
 
+/* The architecture reserves bit 0 for MIPS16 so use bit 1 for descriptors.  */
+#undef TARGET_CUSTOM_FUNCTION_DESCRIPTORS
+#define TARGET_CUSTOM_FUNCTION_DESCRIPTORS 2
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-mips.h"