Workaround 'argument to function is always 1' cppcheck false positives

Workaround 'argument to function is always 1' cppcheck false positives

* allchblk.c (GC_print_hblkfreelist): Replace "while(p!=0)" with
"while(p)"; add a marker that the change is for cppcheck.
* allchblk.c (GC_free_block_ending_at, GC_add_to_fl, GC_split_block,
GC_allochblk_nth, GC_freehblk): Replace "if(p!=0)" with "if(p)".
* alloc.c (GC_set_fl_marks): Likewise.
* extra/MacOS.c (GC_MacFreeTemporaryMemory): Likewise.
* mallocx.c (GC_generic_malloc_many): Likewise.
* allchblk.c (GC_allochblk_nth): Replace "if(0==p)" with "if(p){}else".
* malloc.c (GC_free): Likewise.
* malloc.c (GC_generic_malloc_uncollectable): Replace
"if(0==p)return 0;<code>;return p;" with "if(p){<code>}return p;".
* mallocx.c (GC_generic_malloc_many): Replace "p+=v;while((p2=*p)!=0)"
with "for(p+=v;(p2=*p)!=0;)".
* reclaim.c (GC_continue_reclaim, GC_reclaim_all): Likewise.