checks for inet_ntoa_r() inet_ntop() and inet_pton()

non-blocking mode, and decouple function detection from function capability.

 and CHECK_FUNC_GETADDRINFO_UNFREEABLE_AI_CANONNAME
internal to CHECK_FUNC_GETADDRINFO

function returns an addrinfo with an unfreeable ai_canonname member ptr.

function returns an addrinfo with an unfreeable ai_addr member ptr.

  Select ANSI C89 dialect plus GNU extensions, again.

  Select precise floating-point model, otherwise doubles are less than 64-bit wide

icc test adjustment:

  Select c89 dialect

  Enable more icc warnings.

  Optimization disabling options used only for icc 9.1

configure is unable of finding out if it has glibc-style or POSIX-style,
trying to ensure that this condition does not go unnoticed.

since these are extremely useful when compiler rejects a set of options.

to the shell echo command are not interpreted when trying to
remove extra whitespace from shell variable content.

  Disable warnings on structure members padding.

  Remove -b from debug-enabled configuration, as Tiny C might have
  been built without the memory and bounds checker support.

  Better disable following warnings when cross-compiling with a gcc older
  than 3.0, to avoid warnings from third party system headers:

    -Wmissing-declarations
    -Wmissing-prototypes
    -Wunused
    -Wshadow

  Disable following warnings when cross-compiling with a gcc older
  than 3.0, to avoid warnings from third party system headers:

    -Wmissing-prototypes
    -Wunused
    -Wshadow

  Do not enable -pedantic when cross-compiling with a gcc older
  than 3.0, to avoid warnings from third party system headers.

  Highest warning level is double -A, next is single -A.
  Due to the big number of warnings these trigger on third
  party header files it is impratical for us to use any of
  them here. If you want them simply define it in CPPFLAGS.

  Warning level reduced from double -A to single -A