Undo old temporary change once used for testing purposes

Symbol hiding configure options renamed to the hopefully less ambiguous
--enable-symbol-hiding and --disable-symbol-hiding as well as related
macro names and some internal variables used for them.

Related configuration file preprocessor symbols named to
CARES_SYMBOL_HIDING and CARES_SYMBOL_SCOPE_EXTERN.

based on the 'visibility' attribute for GNUC and __global for Sun
compilers, taking also in account __declspec function decoration
for Win32 and Symbian DLL's.

Introducing configure options --enable-hidden-symbols and
--disable-hidden-symbols following libcurl's naming.

renamed generated config.h to ares_config.h in order to avoid clashes when libcurl is used with other projects which also have a config.h.

systems which support external, undefined, symbols in shared libraries.

Moved *_CHECK_COMPILER_HALT_ON_ERROR and *_CHECK_COMPILER_ARRAY_SIZE_NEGATIVE to *-compilers.m4 along with other *_CHECK_COMPILER_*

the socklen_t issue on this platform.

  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

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.