mod_php5.c is the statically compiled php module. So when you compiled php, you added it as a staticly linked object, instead of a dynamic shared object (DSO).
A DSO will have the extension .so for "shared object" which is the typical way PHP is loaded (so that you can just uncomment the line LoadModule php5_module ... to remove php). You can compile php into Apache so it can't be unloaded "accidentally" and that's when you get mod_php5.c
So if you've compiled PHP to be a shared object (loaded at Apache start-up), then you'd want to look for libphp5.so. If it's a static link, you can look for the module mod_php5.c. Understand?