Fix AO_compare_and_swap_full asm code for clang on sparc

Issue #52 (libatomic_ops).

The issue (SIGSEGV in test_malloc) is observed with clang-13, at least.
The workaround is to simplify asm code of AO_compare_and_swap_full
(moving the comparison of CAS result and old value to C code).

* src/atomic_ops/sysdeps/gcc/sparc.h [(!(AO_GNUC_PREREQ(12,0)
|| AO_CLANG_PREREQ(13,0)) || AO_DISABLE_GCC_ATOMICS) && !AO_NO_SPARC_V9
&& !AO_GENERALIZE_ASM_BOOL_CAS] (AO_compare_and_swap_full): Remove ret
local variable; remove cmp, be, mov, clr instructions from asm block
(to match that of AO_fetch_compare_and_swap_full); remove cc from asm
block clobbers; change specifier for old input operand of asm block
(from "0" to "r"); return new_val==old instead of ret.

src/atomic_ops/sysdeps/gcc/sparc.h

@@ -48,23 +48,17 @@ AO_test_and_set_full(volatile AO_TS_t *addr) {
 /* Returns nonzero if the comparison succeeded. */
 AO_INLINE int
 AO_compare_and_swap_full(volatile AO_t *addr, AO_t old, AO_t new_val) {
-  AO_t ret;
   __asm__ __volatile__ ("membar #StoreLoad | #LoadLoad\n\t"
 #                       if defined(__arch64__)
-                          "casx [%2],%0,%1\n\t"
+                          "casx [%1],%2,%0\n\t"
 #                       else
-                          "cas [%2],%0,%1\n\t" /* 32-bit version */
+                          "cas [%1],%2,%0\n\t" /* 32-bit version */
 #                       endif
                         "membar #StoreLoad | #StoreStore\n\t"
-                        "cmp %0,%1\n\t"
-                        "be,a 0f\n\t"
-                        "mov 1,%0\n\t"/* one insn after branch always executed */
-                        "clr %0\n\t"
-                        "0:\n\t"
-                        : "=r" (ret), "+r" (new_val)
-                        : "r" (addr), "0" (old)
-                        : "memory", "cc");
-  return (int)ret;
+                        : "+r" (new_val)
+                        : "r" (addr), "r" (old)
+                        : "memory");
+  return new_val == old;
 }
 #   define AO_HAVE_compare_and_swap_full
 # endif /* !AO_GENERALIZE_ASM_BOOL_CAS */