feature: C89 adherence #60

Job	Run time
Build C89 (5.1.5)	17s
Build C89 (5.2.4)	11s
Build (5.1, windows-latest)	30s
MSYS2 Build (mingw64, x86_64, 5.4, lua, lua)	2s
Build C89 (5.3.6)	13s
Build (5.1, ubuntu-latest)	37s
MSYS2 Build (mingw64, x86_64, 5.3, lua53, lua5.3)	2s
Build C89 (5.4.7)	15s
Build (5.1, macos-latest)	19s
MSYS2 Build (mingw64, x86_64, 5.1, lua51, lua5.1)	1s
Build (5.2, windows-latest)	23s
MSYS2 Build (mingw64, x86_64, 5.1, luajit, luajit)	1s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.4, lua, lua)	1s
Build (5.2, ubuntu-latest)	17s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.3, lua53, lua5.3)	1s
Build (5.2, macos-latest)	24s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.1, lua51, lua5.1)	1s
Build (5.3, windows-latest)	25s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.1, luajit, luajit)	1s
Build (5.3, ubuntu-latest)	24s
MSYS2 Build (clang64, clang-x86_64, 5.4, lua, lua)	3s
Build (5.3, macos-latest)	16s
MSYS2 Build (clang64, clang-x86_64, 5.3, lua53, lua5.3)	24s
Build (5.4, windows-latest)	47s
MSYS2 Build (clang64, clang-x86_64, 5.1, lua51, lua5.1)	8s
Build (5.4, ubuntu-latest)	35s
Build (5.4, macos-latest)	19s
MSYS2 Build (clang64, clang-x86_64, 5.1, luajit, luajit)	25s
Build (luajit, windows-latest)	21s
Build (luajit, ubuntu-latest)	12s
Upload rockspec	1s
	7m 56s

Provide feedback