[sanitizer_common] Remove hacks for __builtin_return_address abuse on SPARC

As detailed in Issue llvm#57624, the introduction of
`__builtin_extract_return_address` to `GET_CALLER_PC` in
4248f32
<https://reviews.llvm.org/rG4248f32b9ebe87c7af8ee53911efd47c2652f488> broke
`TestCases/Misc/missing_return.cpp` on Solaris/SPARC.  Unlike most other
targets, the builtin isn't a no-op on SPARC and thus has always been
necessary. Its lack had previously been worked around by calls to
`GetNextInstructionPc` in `sanitizer_stacktrace_sparc.cpp`
(`BufferedStackTrace::UnwindFast`) and `sanitizer_unwind_linux_libcdep.cpp`
(`BufferedStackTrace::UnwindSlow`).  However, those calls are superfluous
now and actually harmful.

This patch removes those hacks, fixing the failure.

Tested on `sparcv9-sun-solaris2.11` and on `sparc-sun-solaris2.11` in the
GCC tree.  On the latter, several more testcase failures had been caused by
this issue since ASan actually works with `gcc` on SPARC, unlike `clang`.

Differential Revision: https://reviews.llvm.org/D156504

(cherry picked from commit 679c076)

Author: rorth

compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_sparc.cpp

@@ -30,13 +30,7 @@ void BufferedStackTrace::UnwindFast(uptr pc, uptr bp, uptr stack_top,
   // TODO(yln): add arg sanity check for stack_top/stack_bottom
   CHECK_GE(max_depth, 2);
   const uptr kPageSize = GetPageSizeCached();
-#if defined(__GNUC__)
-  // __builtin_return_address returns the address of the call instruction
-  // on the SPARC and not the return address, so we need to compensate.
-  trace_buffer[0] = GetNextInstructionPc(pc);
-#else
   trace_buffer[0] = pc;
-#endif
   size = 1;
   if (stack_top < 4096) return;  // Sanity check for stack top.
   // Flush register windows to memory

compiler-rt/lib/sanitizer_common/sanitizer_unwind_linux_libcdep.cpp

@@ -139,13 +139,7 @@ void BufferedStackTrace::UnwindSlow(uptr pc, u32 max_depth) {
   if (to_pop == 0 && size > 1)
     to_pop = 1;
   PopStackFrames(to_pop);
-#if defined(__GNUC__) && defined(__sparc__)
-  // __builtin_return_address returns the address of the call instruction
-  // on the SPARC and not the return address, so we need to compensate.
-  trace_buffer[0] = GetNextInstructionPc(pc);
-#else
   trace_buffer[0] = pc;
-#endif
 }
 
 void BufferedStackTrace::UnwindSlow(uptr pc, void *context, u32 max_depth) {