Fix for ppc64le

Summary:
Inlining `getStackTraceInPlace` fails on Fedora with

```
/builddir/build/BUILD/folly-2020.12.21.00/folly/experimental/symbolizer/StackTrace.cpp: In function 'folly::symbolizer::(anonymous namespace)::getStackTraceInPlace(ucontext_t&, unw_cursor&, unsigned long*, unsigned long)':
/builddir/build/BUILD/folly-2020.12.21.00/folly/experimental/symbolizer/StackTrace.cpp:88:9: error: function 'folly::symbolizer::(anonymous namespace)::getStackTraceInPlace(ucontext_t&, unw_cursor&, unsigned long*, unsigned long)' can never be inlined because it uses setjmp
   88 | ssize_t getStackTraceInPlace(
      |         ^~~~~~~~~~~~~~~~~~~~
```

Reviewed By: yfeldblum

Differential Revision: D29639503

fbshipit-source-id: 823692d95171d5fb3968761c00b4cc5650db171b

folly/experimental/symbolizer/StackTrace.cpp

@@ -86,7 +86,11 @@ inline bool getFrameInfo(unw_cursor_t* cursor, uintptr_t& ip) {
   return true;
 }
 
+// on ppc64le, fails with
+// function can never be inlined because it uses setjmp
+#if FOLLY_PPC64 == 0
 FOLLY_ALWAYS_INLINE
+#endif
 ssize_t getStackTraceInPlace(
     unw_context_t& context,
     unw_cursor_t& cursor,