Description of problem:
The pkg-config file contains an invalid library path on x86_64 systems. The line
in /usr/lib64/pkgconfig/lua.pc reads:
libdir=${exec_prefix}/lib

while in fact it should read:
libdir=${exec_prefix}/lib64

This causes warnings like
/usr/bin/ld: skipping incompatible /usr/lib/liblua.so when searching for -llua
when linking against the Lua runtime lib while using "pkg-config --libs lua".

Version-Release number of selected component (if applicable):
lua-5.1.2-1.fc8
lua-devel-5.1.2-1.fc8

How reproducible:
Always

Steps to Reproduce:
1. Create trivialmain.c with:
int main(int argc, char **argv) { return 0; }
2. Compile and link against Lua with:
gcc -o trivialmain `pkg-config --libs lua` trivialmain.c
  
Actual results:
Warnings produced since ld now search /usr/lib for *any* library.

Expected results:
No warnings, /usr/lib should not be searched on x86_64 systems.