hwasan_symbolize: warn about missing symbols at most once per library

[merge_guards_bot]

Unit tests: pass. 62310 tests passed, 0 failed and 838 were skipped.

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

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compiler-rt/lib/hwasan/scripts/hwasan_symbolize

 
 class Symbolizer:
   def __init__(self, path, binary_prefixes, paths_to_cut):
     self.__pipe = None
     self.__path = path
     self.__binary_prefixes = binary_prefixes
     self.__paths_to_cut = paths_to_cut
     self.__log = False
+    self.__warnings = set()
 
   def enable_logging(self, enable):
     self.__log = enable
 
   def __open_pipe(self):
     if not self.__pipe:
       self.__pipe = subprocess.Popen([self.__path, "-inlining", "-functions"],
                                      stdin=subprocess.PIPE, stdout=subprocess.PIPE)
for p in self.__binary_prefixes:
       full_path = os.path.join(p, name)
       if os.path.exists(full_path):
         return full_path
     # Try stripping extra path components as the last resort.
     for p in self.__binary_prefixes:
       full_path = os.path.join(p, os.path.basename(name))
       if os.path.exists(full_path):
         return full_path
+    if name not in self.__warnings:
       print >>sys.stderr, "Could not find symbols for", name
+      self.__warnings.add(name)
     return None
 
   def iter_locals(self, binary, addr):
     self.__open_pipe()
     p = self.__pipe
     binary = self.__process_binary_name(binary)
     if not binary:
       return