Replace makefile with shell script

Replace makefile with shell script

We needed to replace make,
because it does not work when filenames contain spaces.
Also, the makefile was for GNU make, thus not POSIX.
It is replaced with a script for sh, the POSIX shell.
The script build.sh [args...] executes [args...]
on each “.c” file in src/.
To compile using gcc and the option “-O3”,
run “./build.sh gcc -O3”.
Executing build.sh without arguments compiles using
“clang -DNDEBUG -ferror-limit=1 -flto -fvisibility=hidden
-march=native -O3 -s -static -std=c11 -Werror -Weverything
-Wno-disabled-macro-expansion -Wno-reserved-id-macro”.