More NetWare build tweaks.

Make use of CFLAGS from environment.
Added default maxerrors value 1 so that the compiler breaks
after 1st error; can be overwritten with CC_MAX_ERRORS var.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@1484176 13f79535-47bb-0310-9956-ffa450edef68