configure: split has_or_abort in two: one to check, one to abort

Split the has_or_abort function in two:
- one that checks if the tool if found,
- one that calls the above check, and aborts if not found

The rational behind this is to be able to check for a tool
and if not found, fallback to using our bundled version,
should the need arise (and I get time).

 --- gcc-4.0.0/libstdc++-v3/include/c_std/std_cstdio.h-orig	2005-04-29 00:08:41.000000000 -0500

 +++ gcc-4.0.0/libstdc++-v3/include/c_std/std_cstdio.h	2005-04-29 00:08:45.000000000 -0500

 @@ -142,7 +142,7 @@

    using ::vsprintf;

  }

 -#if _GLIBCXX_USE_C99

 +#if _GLIBCXX_USE_C99 || defined(__UCLIBC__)

  #undef snprintf

  #undef vfscanf