TM4C123 Header File Problem
First, you should always add all the library files to the project. Everything. Headers and source files included. In fact, it would be best if you started from a new project and installed the Device Family Pack as instructed. Follow Keil and Tiva instructions or any online tutorials to the letter. Only after you've successfully built an application using the standard procedures, to do basic stuff like blink an LED, should you then begin tinkering with the build process, as you're doing. For now, you do not know enough yet or have a reference "working" setup.

Second, the include errors you're getting are likely because you haven't configured your include paths. Based on your image, you did not maintain the original library structure but instead copied the header files directly to the same folder as your main.c, thus those headers are found automatically when compiling main.c but can't be seen by any other source file that isn't in that folder, especially when they're looking for inc/hw_memmap.h for instance. Do not mistake the internal Keil IDE folder structure for the actual folder structure on disk; these two have little to do with each other.

You need to inform Keil (as with most other IDEs) about where to look for header files. 


Delete those library headers that you have copied directly to main.c's folder. main.c should be the only file with code left in that folder.
I think I can see you already have the Device Family Pack included in your project. Clicking the Device item on the left should show all the library source files. If it doesn't, then add the library, following Keil instructions. Probably best done from a new project, as I said earlier.
This answer here explains how to add the include paths to your project settings. This step is necessary for every project you create. The important paths you need to add are: inc/ and driverlib/. Supply the absolute paths, i.e. C:/..., to be sure.


If you try to build now and get the Undefined symbol linker errors again, it means you still don't have those library source files present in your project.