Description of problem:

conky's configure cannot find lua on EPEL7 because it looks for it incorrectly:

configure:13975: checking for LUA
configure:13983: $PKG_CONFIG --exists --print-errors "lua == 5.1"
Unknown version comparison operator '==' after package name 'lua' in file '(command line arguments)'

The proper operator is "=".

Also, the lua package in RHEL7 only provides lua.pc, not lua-5.1.pc, which is how it works in Fedora:

configure:14018: checking for LUA51
configure:14026: $PKG_CONFIG --exists --print-errors "lua-5.1 >= 5.1"
configure:14029: $? = 0

This should fix:

--- configure.ac.in.pkgconfig   2014-06-17 18:23:33.000000000 -0600
+++ configure.ac.in     2015-01-30 11:57:28.557584338 -0700
@@ -488,7 +488,7 @@

 AM_CONDITIONAL(BUILD_LUA, test x$want_lua = xyes)
 if test x$want_lua = xyes; then
-       PKG_CHECK_MODULES(LUA, lua == 5.1, [ ],[
+       PKG_CHECK_MODULES(LUA, lua = 5.1, [ ],[
                PKG_CHECK_MODULES(LUA51, lua-5.1 >= 5.1, [ ],[
                        PKG_CHECK_MODULES(LUA51, lua5.1 >= 5.1)
                ])