message: update `-rdynamic` usage
  Summary:
  rdynamic gives us more readable stack traces (function names instead of
  addresses)
  * Add -rdynamic for OSS
  * simplify usage in BUCK
  * The previous version couldn't actually append correctly anyway,
  So, might as well write the flag in directly.
diff: @@ -219,6 +219,9 @@ redex_all_LDADD = \
  $(BOOST_REGEX_LIB) \
  -lpthread
  +redex_all_LDFLAGS = \
  + -rdynamic # function names in stack traces
  +
  redexdump_SOURCES = \
  tools/redexdump/DumpTables.cpp \
  tools/redexdump/PrintUtil.cpp \
  