OS400/makefile.sh: fix shellcheck warning SC2038 differently #1

Job	Run time
cygwin, CM x86_64 openssl	6m 55s
cygwin, AM x86_64 openssl R	8m 20s
linux-mingw, AM gcc	2m 9s
linux-mingw, CM gcc	59s
linux-mingw, CM clang-tidy	5m 15s
dl-mingw, CM 6.4.0-i686 schannel !unity	1m 37s
msvc, CM arm64-windows schannel U	8m 48s
dl-mingw, CM 9.5.0-x86_64 schannel	7m 52s
dl-mingw, CM 7.3.0-x86_64 schannel mbedtls U	1m 39s
dl-mingw, CM 15.1.0-x86_64 schannel	2m 42s
msvc, CM x64-windows openssl +examples	6m 41s
msvc, CM x64-uwp !ssl +examples	2m 26s
msys2, AM x86_64 default	4m 59s
msys2, AM x86_64 !proxy	8m 39s
mingw, AM x86_64 default XP	6m 23s
mingw, AM x86_64 c-ares U	11m 22s
msys2, AM x86_64 default R	7m 26s
mingw, CM clang-x86_64 gnutls libssh	43s
mingw, CM clang-aarch64 schannel R TrackMemory	3m 42s
mingw, CM x86_64 schannel c-ares U	8m 19s
mingw, CM x86_64 schannel dev debug	3m 19s
msys2, CM x86_64 default	7m 24s
mingw, CM clang-x86_64 openssl	3m 10s
mingw, CM i686 schannel R	2m 49s
mingw, CM ucrt-x86_64 schannel uwp	2m 47s
dl-mingw, CM 4.8.1-x86_64 schannel !examples	59s
	2h 7m 24s

Provide feedback