[nolibc] Make SymbolizerPrepareForSandboxing weak and optional.

Differential Revision: http://llvm-reviews.chandlerc.com/D872

llvm-svn: 182765

compiler-rt/lib/sanitizer_common/sanitizer_linux.cc

@@ -307,7 +307,8 @@ void PrepareForSandboxing() {
   // cached mappings.
   MemoryMappingLayout::CacheMemoryMappings();
   // Same for /proc/self/exe in the symbolizer.
-  SymbolizerPrepareForSandboxing();
+  if (&SymbolizerPrepareForSandboxing)
+    SymbolizerPrepareForSandboxing();
 }
 
 // ----------------- sanitizer_procmaps.h

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer.h

@@ -114,7 +114,7 @@ typedef bool (*string_predicate_t)(const char *);
 uptr GetListOfModules(LoadedModule *modules, uptr max_modules,
                       string_predicate_t filter);
 
-void SymbolizerPrepareForSandboxing();
+void SymbolizerPrepareForSandboxing() SANITIZER_WEAK_ATTRIBUTE;
 
 }  // namespace __sanitizer