libpq.so.2.0 brings compilation problems

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Patrick LUCIEN
Your email address :
stephane(dot)dacremont(at)libertysurf(dot)fr

System Configuration
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Architecture (example: Intel Pentium) : Intel
Pentium

processor : 450
vendor_id : Intel
cpu family : 6
model :
model name : Pentium 3
stepping :
fdiv_bug :
hlt_bug :
sep_bug :
f00f_bug :
coma_bug :
fpu :
fpu_exception :
cpuid level :
wp :
flags :
bogomips :

Operating System (example: Linux 2.0.26 ELF) :

Linux Mandrake6.0 (based on RedHat6.0) 2.2.x

PostgreSQL version (example: PostgreSQL-6.5.1):

PostgreSQL-6.4.2

Compiler used (example: gcc 2.8.0) :

gcc (almost certainly a recent version)

Libc version :

?

Please enter a FULL description of your problem:
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Compiling a C program using the libpq library fails.
I get the error:

/usr/lib/libpq.so:undefined symbol crypt

I use libpq.so.2.0 as furnished in a RPM package:
postgresql-6.4.2-devel...

Please describe a way to repeat the problem. Please try to
provide a
concise reproducible example, if at all possible:
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any C program using libpq will do the job.

If you know how this problem might be fixed, list the solution
below:
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