build: remove -Werror when running ./configure
Building with CFLAGS="-Werror -Wall" caused configure to fail due to
the following warnings being converted to errors:
* conflicting types for built-in function
* unused variable
When these warnings get converted to errors, they prevent the detection
of fork, isascii, isinf, isnan, math libs, long long & struct flock.
Add -Wno-error in this case to prevent these warnings being treated as errors.
Reported-by: Evan Hunter <evan@ozhiker.com>
Signed-off-by: Steve Bennett <steveb@workware.net.au>