[autotools] Adding malloc configure test?

[Gilles Ganault]

Hello

        I'm no configure/make expert, and need to cross-compile SSHGuard to
run on a uClinux-based applianced.

After successfully (?) running "configure", make stops after a few
seconds:
==========
... 
/usr/src/baps/opt/uClinux/bfin-linux-uclibc/bin/bfin-linux-uclibc-gcc
-I. -O2 -Wall -std=c99  -D_XOPEN_SOURCE  -O2 -Wall -pedantic
-I/usr/src/baps/uClinux-dist/linux-2.6.x/include
-I/usr/src/baps/uClinux-dist/staging/usr/include   -o sshguard
sshguard.o seekers.o sshguard_whitelist.o sshguard_log.o
sshguard_procauth.o sshguard_blacklist.o sshguard_options.o
sshguard_logsuck.o simclist.o hash_32a.o parser/libparser.a
fwalls/libfwall.a -lpthread 

sshguard_options.o: In function `.L17': 
sshguard_options.c:(.text+0x1d0): undefined reference to `_rpl_malloc'
fwalls/libfwall.a(command.o): In function `_run_command': 
==========

The problem is solved by exporting this variable before running
"configure":
==========
export ac_cv_func_malloc_0_nonnull=yes
==========

But I'd like to know how to solve this problem more elegantly: Where
should I put this type of settings?

Thank you.