[libunwind] Define _Unwind_Backtrace for powerpc, sparc

Add SPARC to the list of platforms for which we provide a full
unwind implementation which leads to _Unwind_Backtrace being defined within
libunwind.so.

Likewise for PPC (see D118320 for background).

Reviewed By: #libunwind, MaskRay, Arfrever

Differential Revision: https://reviews.llvm.org/D119068

Author: thesamesam

libunwind/src/config.h

@@ -109,13 +109,10 @@
 #define _LIBUNWIND_SUPPORT_FRAME_APIS
 #endif
 
-#if defined(__i386__) || defined(__x86_64__) ||                                \
-    defined(__ppc__) || defined(__ppc64__) || defined(__powerpc64__) ||        \
-    (!defined(__APPLE__) && defined(__arm__)) ||                               \
-    defined(__aarch64__) ||                                                    \
-    defined(__mips__) ||                                                       \
-    defined(__riscv) ||                                                        \
-    defined(__hexagon__)
+#if defined(__i386__) || defined(__x86_64__) || defined(__powerpc__) ||        \
+    (!defined(__APPLE__) && defined(__arm__)) || defined(__aarch64__) ||       \
+    defined(__mips__) || defined(__riscv) || defined(__hexagon__) ||           \
+    defined(__sparc__)
 #if !defined(_LIBUNWIND_BUILD_SJLJ_APIS)
 #define _LIBUNWIND_BUILD_ZERO_COST_APIS
 #endif