Add C99 build option to example users #1617

Job	Run time
build (mobc) / Build for linux32 (gcc, Wextra)	43s
build (mobc) / Build as C++ for linux32	24s
build (mobc) / Build for Win32 by MSVC	1m 15s
build (mobc) / Build as C++ for Win32 by MSVC++	1m 17s
build (mobc) / Build for linux32 (clang, Werror)	1m 5s
build (mobc) / Build for linux32 (clang, Wextra)	1m 12s
build (subobc) / Build for linux32 (gcc, Wextra)	23s
build (subobc) / Build as C++ for linux32	1m 8s
build (subobc) / Build for linux32 (clang, Werror)	1m 7s
build (subobc) / Build for Win32 by MSVC	1m 13s
build (subobc) / Build as C++ for Win32 by MSVC++	1m 29s
build (subobc) / Build for linux32 (clang, Wextra)	41s
	11m 57s

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