[libunwind] Remove compatibility support for macOS 10.6

[steven_wu]

Summary

Remove _dyld_find_unwind_sections implementation for macOS that is
10.6 or previous. 10.6 is no longer supported for TOT libunwind after
removing its libkeymgr dependency.

[pete]

LGTM

[mstorsjo]

LGTM

libunwind/src/AddressSpace.hpp

#ifdef __APPLE__
   struct dyld_unwind_sections
   {
     const struct mach_header*   mh;
     const void*                 dwarf_section;
     uintptr_t                   dwarf_section_length;
     const void*                 compact_unwind_section;
     uintptr_t                   compact_unwind_section_length;
   };
-  #if (defined(__MAC_OS_X_VERSION_MIN_REQUIRED) \
-                                 && (__MAC_OS_X_VERSION_MIN_REQUIRED >= 1070)) \
-      || defined(__IPHONE_OS_VERSION_MIN_REQUIRED)
-    // In 10.7.0 or later, libSystem.dylib implements this function.
-    extern "C" bool _dyld_find_unwind_sections(void *, dyld_unwind_sections *);
-  #else
-    // In 10.6.x and earlier, we need to implement this functionality. Note
-    // that this requires a newer version of libmacho (from cctools) than is
-    // present in libSystem on 10.6.x (for getsectiondata).
-    static inline bool _dyld_find_unwind_sections(void* addr,
-                                                    dyld_unwind_sections* info) {
-      // Find mach-o image containing address.
-      Dl_info dlinfo;
-      if (!dladdr(addr, &dlinfo))
-        return false;
-#if __LP64__
-      const struct mach_header_64 *mh = (const struct mach_header_64 *)dlinfo.dli_fbase;
-#else
-      const struct mach_header *mh = (const struct mach_header *)dlinfo.dli_fbase;
-#endif
-
-      // Initialize the return struct
-      info->mh = (const struct mach_header *)mh;
-      info->dwarf_section = getsectiondata(mh, "__TEXT", "__eh_frame", &info->dwarf_section_length);
-      info->compact_unwind_section = getsectiondata(mh, "__TEXT", "__unwind_info", &info->compact_unwind_section_length);
-
-      if (!info->dwarf_section) {
-        info->dwarf_section_length = 0;
-      }
-
-      if (!info->compact_unwind_section) {
-        info->compact_unwind_section_length = 0;
-      }
-
-      return true;
-    }
-  #endif
+
 
 #elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL)
 
 // When statically linked on bare-metal, the symbols for the EH table are looked
 // up without going through the dynamic loader.
 
 // The following linker script may be used to produce the necessary sections and symbols.
 // Unless the --eh-frame-hdr linker option is provided, the section is not generated