Cannot install -- "/lib/cpp" failed sanity check

I am trying to configure the PGSQL 8.1RC and here is my error
log, I'd appreciate any ideas, thanks!

-shell$ ./configure
checking build system type... i686-pc-linux-gnulibc1
checking host system type... i686-pc-linux-gnulibc1
checking which template to use... linux
checking whether to build with 64-bit integer date/time
support... no
checking whether NLS is wanted... no
checking for default port number... 5432
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ANSI C... none needed
checking if gcc supports -Wdeclaration-after-statement... yes
checking if gcc supports -Wendif-labels... no
checking if gcc supports -fno-strict-aliasing... yes
configure: using CFLAGS=-O2 -Wall -Wmissing-prototypes
-Wpointer-arith -Winline
-Wdeclaration-after-statement -fno-strict-aliasing
checking whether the C compiler still works... yes
checking how to run the C preprocessor... /lib/cpp
configure: error: C preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details.

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