building: Add prerequisite steps for Arch Linux

Install all needed dependencies and either gcc or clang
building: Change compiler to compiler suite

This is because previously configure was failing with these errors:

configure: error: unknown compiler suite: clang++. manually specify
--c-compiler and --cpp-compiler, or use one of [llvm, gnu]

configure: error: unknown compiler suite: g++. manually specify
--c-compiler and --cpp-compiler, or use one of [llvm, gnu]
building: Change path to variable

Here path has to be absolute, or start with absolute path environment
variable. This is because make was failing with this error:

you need to specify AGE2DIR (e.g. /home/user/.wine/drive_c/age).
Makefile:37: recipe for target 'media' failed
make: *** [media] Error 1