I've successfully build 4.5.3 on Solaris x86

[Renny Koshy]

uname -a :
SunOS devsolx86 5.10 Generic_139556-08 i86pc i386 i86pc Solaris

config.guess output:
i386-pc-solaris2.10

gcc -v output:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/export/usr_local/gcc4/bin/../libexec/gcc/i386-pc-solaris2.10/4.5.3/lto-wrapper
Target: i386-pc-solaris2.10
Configured with: ../configure --with-gnu-as --with-as=/usr/sfw/bin/gas
--without-gnu-ld --with-ld=/usr/ccs/bin/ld --enable-shared
--enable-languages=c,c++ --with-gmp=/usr/local --with-mpfr=/usr/local
--prefix=/usr/local/gcc4
Thread model: posix
gcc version 4.5.3 (GCC)

Only enabled C/C++

Had to install mpc-0.8.1 (newer one didn't compile).  used gmp-5.0.2, mpfr-3.0.1