Some systems require unusual options for compilation or linking
that the configure script does not know about.
You can give configure initial values for variables by setting
them in the environment.
Using a Bourne-compatible shell, you can do that on the command line
like this:
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
On systems that have the env program, you can do it like this:
env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
The configuration process uses GCC to build Bash if it is available.