feature: C89 adherence #62

Job	Run time
MSYS2 Build (mingw64, x86_64, 5.4, lua, lua)	43s
Build (5.1, windows-latest)	43s
MSYS2 Build (mingw64, x86_64, 5.3, lua53, lua5.3)	41s
Build C89 (5.1.5)	26s
Build (5.1, ubuntu-latest)	13s
MSYS2 Build (mingw64, x86_64, 5.1, lua51, lua5.1)	43s
Build C89 (5.2.4)	39s
Build (5.1, macos-latest)	22s
Build C89 (5.3.6)	20s
Build (5.2, windows-latest)	19s
MSYS2 Build (mingw64, x86_64, 5.1, luajit, luajit)	41s
Build (5.2, ubuntu-latest)	1s
Build C89 (5.4.7)	23s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.4, lua, lua)	41s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.3, lua53, lua5.3)	44s
Build (5.2, macos-latest)	28s
Build (5.3, windows-latest)	15s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.1, lua51, lua5.1)	42s
MSYS2 Build (ucrt64, ucrt-x86_64, 5.1, luajit, luajit)	40s
Build (5.3, ubuntu-latest)	15s
MSYS2 Build (clang64, clang-x86_64, 5.4, lua, lua)	43s
Build (5.3, macos-latest)	17s
Build (5.4, windows-latest)	1s
MSYS2 Build (clang64, clang-x86_64, 5.3, lua53, lua5.3)	41s
Build (5.4, ubuntu-latest)	1s
MSYS2 Build (clang64, clang-x86_64, 5.1, lua51, lua5.1)	44s
Build (5.4, macos-latest)	35s
Build (luajit, windows-latest)	1s
MSYS2 Build (clang64, clang-x86_64, 5.1, luajit, luajit)	44s
Build (luajit, ubuntu-latest)	1s
Upload rockspec	1s
	13m 48s

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