backtrace: test with DLLs

backtrace: test with DLLs

- tests2/113_btdll.c: test handling multiple stabs infos
Also:
- libtcc.c: remove _ISOC99_SOURCE pre-defines.  It is causing
  strange warnings such as 'strdup not declared'

- i386/x86_64-gen.c cleanup bounds_pro/epilog.  This discards
  the extra code for main's argv.  If needed, __argv might be
  processed instead.

- tccgen.c:block(): reduce stackspace usage.  For example with
  code like "if (..) ... else if (..) ... else if (..)... "
  considerable numbers of nested block() calls may occur.

  Before that most stack space used when compiling itself was
  for libtcc.c:tcc_set_linker().

  Now it's rather this construct at tccpp.c:2765: in next_nomacro1():

  if (!((isidnum_table[c - CH_EOF] & (IS_ID|IS_NUM))
        || c == '.'
        || ((c == '+' || c == '-')
        ...