test #559 tests internal hash create/add/destroy

when allocating/building the fake Curl_addrinfo.

now to minimally exercise some internal hash routines.

  Select ANSI C89 dialect plus GNU extensions, again.

and isn't strictly needed here.

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

icc test adjustment:

  Select c89 dialect

inclusion by the curl tool without colliding with the curl_strequal functions.

  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.

don't have prototypes. They didn't serve any useful purpose here, anyway.

Changed checkprefix() to use it and those instances of strnequal() that
compare host names or other protocol strings that are defined to be
independent of case in the C locale.  This should fix a few more
Turkish locale problems.

  Re-enable all tests for debug-enabled builds.

  For debug-disabled builds only 8 tests are enabled.