make configure try to disable stack protector

in theory we could support stack protector in the libc itself, and
users wanting to experiment with such usage could add
-fstack-protector to CFLAGS intentionally. but to avoid breakage in
the default case, override broken distro-patched gcc that forces stack
protector on.

configure

@@ -263,6 +263,8 @@ tryflag CFLAGS_AUTO -Wno-unused-but-set-variable
 tryflag CFLAGS_AUTO -Wno-unknown-pragmas
 fi
 
+# Some patched GCC builds have these defaults messed up...
+tryflag CFLAGS_AUTO -fno-stack-protector
 tryldflag LDFLAGS_AUTO -Wl,--hash-style=sysv