Workaround 'array compared to 0', 'untrusted loop bound' false defects

Workaround 'array compared to 0', 'untrusted loop bound' false defects
(Cherry-pick commit 36038e1 from 'master' branch.)

* dyn_load.c [SOLARISDL && !USE_PROC_FOR_LIBRARIES]
(GC_FirstDLOpenedLinkMap): Wrap access to dynStructureAddr (which value
obtained from a weak symbol) into COVERT_DATAFLOW() in comparison to 0.
* dyn_load.c [HAVE_DL_ITERATE_PHDR && !DL_ITERATE_PHDR_STRONG]
(GC_register_main_static_data): Wrap access to dl_iterate_phdr weak
symbol into COVERT_DATAFLOW() in comparison to 0.
* dyn_load.c [HAVE_DL_ITERATE_PHDR] (GC_FirstDLOpenedLinkMap): Wrap
access to _DYNAMIC weak symbol into COVERT_DATAFLOW() in comparison to 0.
* include/private/gc_priv.h (TRUSTED_STRING): Pass the argument through
COVERT_DATAFLOW.
* include/private/gcconfig.h (COVERT_DATAFLOW): New macro.
* os_dep.c [SEARCH_FOR_DATA_START] (GC_init_linux_data_start): Wrap
access to __data_start and GC_data_start into COVERT_DATAFLOW() in
comparison to 0.
* tests/disclaim_bench.c: Update comment for include gc_priv.h.
* tests/disclaim_bench.c (main): Pass the integer value obtained from
command-line argument (and which is used as a loop boundary) through
COVERT_DATAFLOW().
* tests/test_cpp.cc (main): Likewise.