Arm64 : Adjust Fortran nested Hack to use bit 1 on aarch64, add to C

This addresses Issue #32 by adjusting the nested function hack to use
bit 1 rather than bit 2.

NOTE: that Arm reserve both bits 0 and 1 for furture use, so that this
is no less a hack than using bit 2 - but it might be a somewhat more
compatible hack.

Tested with the example in Issue #32 (otherwise, there's no real change
in the testsuite).

gcc/c/c-lang.c

@@ -38,6 +38,9 @@ enum c_language_kind c_language = clk_c;
 #undef LANG_HOOKS_INIT_TS
 #define LANG_HOOKS_INIT_TS c_common_init_ts
 
+#undef LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS
+#define LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS true
+
 #if CHECKING_P
 #undef LANG_HOOKS_RUN_LANG_SELFTESTS
 #define LANG_HOOKS_RUN_LANG_SELFTESTS selftest::run_c_tests

gcc/config/aarch64/aarch64.c

@@ -24750,9 +24750,9 @@ aarch64_libgcc_floating_mode_supported_p
 #define TARGET_DWARF_POLY_INDETERMINATE_VALUE \
   aarch64_dwarf_poly_indeterminate_value
 
-/* The architecture reserves bits 0 and 1 so use bit 2 for descriptors.  */
+/* The architecture reserves bits 0 and 1 but hack 1 for now.  */
 #undef TARGET_CUSTOM_FUNCTION_DESCRIPTORS
-#define TARGET_CUSTOM_FUNCTION_DESCRIPTORS 4
+#define TARGET_CUSTOM_FUNCTION_DESCRIPTORS 2
 
 #undef TARGET_HARD_REGNO_NREGS
 #define TARGET_HARD_REGNO_NREGS aarch64_hard_regno_nregs

gcc/config/aarch64/aarch64.h

@@ -69,9 +69,7 @@
 
 #define STACK_BOUNDARY		128
 
-/* Custom function descriptors use bit 2 so function alignment must be
-   at least 64 to work with this.  */
-#define FUNCTION_BOUNDARY	64
+#define FUNCTION_BOUNDARY	32
 
 #define EMPTY_FIELD_BOUNDARY	32