gddrescue: Do not build with uClibc-ng

gddrescue: Do not build with uClibc-ng

From the developer:

It seems that uClibc-ng is defining fgetc, fputc, feof, and ferror as
macros and not including them in std.

IMO this is a bug in uClibc-ng (maybe caused by lack of clarity in the
C++ standard), because even the C functions that are alowed to be
defined as macros (putc, getc) should be included in std for
consistency. Just imagine the chaos if std::getc were defined or
undefined depending on how it is implemented.

Signed-off-by: Rosen Penev <rosenp@gmail.com>