protobuf-c does not compile on 64bit Solaris 11

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What steps will reproduce the problem?
1. Try and compile on 64bit Solaris/OpenIndiana 11

What is the expected output? What do you see instead?
It should compile cleanly. Instead, the program fails to compile with an 
ambiguous linker error.

This is because the build system determines the environment with uname -p. On 
Solaris 11, even on 64bit this yields i386. With isainfo -b, it becomes clear 
that it's a 64bit machine.

What version of the product are you using? On what operating system?
Latest protobuf, Oracle Solaris 11, gcc 4.5

Please provide any additional information below.
A workaround for now is to manually set CFLAGS and CXXFLAGS to -m64.

Original issue reported on code.google.com by ay1244 on 20 Jan 2013 at 3:01