filesetup: clear O_RDWR flag for verify_only write workloads #735

Job	Run time
build (linux-gcc)	9m 6s
build (linux-gcc)	9m 6s
build (linux-clang)	9m 45s
build (linux-clang)	9m 45s
build (macos)	7m 44s
build (macos)	9m 36s
build (linux-i686-gcc)	8m 20s
build (linux-i686-gcc)	8m 20s
build (android)	36s
build (android)	36s
build (windows-cygwin-64)	12m 24s
build (windows-cygwin-64)	12m 24s
build (windows-cygwin-32)	12m 6s
build (windows-cygwin-32)	12m 6s
build (windows-msys2-64)	10m 13s
build (windows-msys2-64)	10m 13s
build (android-recovery, ubuntu-22.04, aarch64-linux-android32)	32s
build (android-recovery, ubuntu-22.04, aarch64-linux-android32)	32s
	2h 23m 24s

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